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N-2 - USD ($) | 3 Months Ended | 12 Months Ended |  |  |  |  |  |  |  |
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Aug. 31, 2025 | May 31, 2025 | Feb. 28, 2025 | Nov. 30, 2024 | Aug. 31, 2024 | May 31, 2024 | Feb. 29, 2024 | Nov. 30, 2023 | Aug. 31, 2025 | Aug. 31, 2023 | Aug. 31, 2022 | Aug. 31, 2021 | Aug. 31, 2020 | Aug. 31, 2019 | Aug. 31, 2018 | Aug. 31, 2017 | Aug. 31, 2016
Cover [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Entity Central Index Key |  |  |  |  |  |  |  |  |  |  | 0000892992 |  |  |  |  |  |  |  |
Amendment Flag |  |  |  |  |  |  |  |  |  |  | false |  |  |  |  |  |  |  |
Document Type |  |  |  |  |  |  |  |  |  |  | N-CSR |  |  |  |  |  |  |  |
Entity Registrant Name |  |  |  |  |  |  |  |  |  |  | Nuveen Arizona Quality Municipal Income Fund |  |  |  |  |  |  |  |
Fee Table [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shareholder Transaction Expenses [Table Text Block] |  |  |  |  |  |  |  |  |  |  | SUMMARY OF FUND EXPENSES The purpose of the tables and the example below are to help you understand all fees and expenses that you, as a common shareholder, would bear directly or indirectly. The tables show the expenses of the Fund as a percentage of the average net assets applicable to Common Shares and not as a percentage of total assets or managed assets.
Shareholder Transaction Expenses |  | NAZ |  | NKX |  | NAC |  | NAN
Maximum Sales Charge (as a percentage of offering price) (1) |  | 1.00% |  | 1.00% |  | 1.00% |  | 1.00%
Dividend Reinvestment Plan Fees (2) |  | $2.50 |  | $2.50 |  | $2.50 |  | $2.50
(1) | The maximum sales charge for offerings made at-the-market is 1.00%. If the Common Shares are sold to or through underwriters in an offering that is not made at-the-market, the applicable Prospectus Supplement will set forth any other applicable sales load. Additionally, the applicable Prospectus Supplement will set forth the offering expenses (if any) borne by Fund common shareholders.
(2) | You will be charged a $2.50 service charge and pay brokerage charges if you direct Computershare Inc. and Computershare Trust Company, N.A., as agent for the common shareholders, to sell your Common Shares held in a dividend reinvestment account.
Sales Load [Percent] | [1] |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |  |
Dividend Reinvestment and Cash Purchase Fees | [2] |  |  |  |  |  |  |  |  |  | $ 2.50 |  |  |  |  |  |  |  |
Other Transaction Expenses [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual Expenses [Table Text Block] |  |  |  |  |  |  |  |  |  |  |
Annual Expenses (As a Percentage of Net Assets Attributable to Common Shares) (1) |  |  | NAZ |  |  |  | NKX |  |  |  | NAC |  |  |  | NAN |
Management Fees |  |  | 0.98% |  |  |  | 0.99% |  |  |  | 0.95% |  |  |  | 0.98% |
Interest and Other Related Expenses (2) |  |  | 2.43% |  |  |  | 2.68% |  |  |  | 2.78% |  |  |  | 2.67% |
Other Expenses (3) |  |  | 0.14% |  |  |  | 0.10% |  |  |  | 0.06% |  |  |  | 0.12% |
Total Annual Expenses |  |  | 3.55% |  |  |  | 3.77% |  |  |  | 3.79% |  |  |  | 3.77% |
(1) | Stated as percentages of average net assets attributable to Common Shares for the fiscal year ended August 31, 2025.
(2) | Interest and Other Related Expenses reflect actual expenses and fees for leverage incurred by a Fund for the fiscal year ended August 31, 2025. The types of leverage used by the Fund during the fiscal year ended August 31, 2025 are described in the Fund Leverage and the Notes to Financial Statements sections of this annual report. Actual Interest and Other Related Expenses incurred in the future may be higher or lower. If short-term market interest rates rise in the future, and if the Fund continues to maintain leverage, the cost of which is tied to short-term interest rates, the Fund’s interest expenses on its short-term borrowings can be expected to rise in tandem. The Fund’s use of leverage will increase the amount of management fees paid to the Fund’s adviser and sub-advisor(s).
(3) | Other Expenses are based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%.
Management Fees [Percent] | [3] |  |  |  |  |  |  |  |  |  | 0.98% |  |  |  |  |  |  |  |
Interest Expenses on Borrowings [Percent] | [3],[4] |  |  |  |  |  |  |  |  |  | 2.43% |  |  |  |  |  |  |  |
Other Annual Expenses [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other Annual Expenses [Percent] | [3],[5] |  |  |  |  |  |  |  |  |  | 0.14% |  |  |  |  |  |  |  |
Total Annual Expenses [Percent] | [3] |  |  |  |  |  |  |  |  |  | 3.55% |  |  |  |  |  |  |  |
Expense Example [Table Text Block] |  |  |  |  |  |  |  |  |  |  | Example The following example illustrates the expenses, including the applicable transaction fees (referred to as the “Maximum Sales Charge” in the Shareholder Transaction Expenses table above), if any, that a common shareholder would pay on a $1,000 investment that is held for the time periods provided in the table. The example assumes that all dividends and other distributions are reinvested in the Fund and that the Fund’s Annual Expenses, as provided above, remain the same. The example also assumes a 5% annual return. Actual expenses may be greater or less than those assumed. Moreover, the Fund’s actual rate of return may be greater or less than the hypothetical 5% return shown in the example. Example # 1 (At-the-Market Transaction) The following example assumes a transaction fee of 1.00%, as a percentage of the offering price.
|  | 1 Year |  |  | 3 Years |  |  | 5 Years |  |  | 10 Years |
NAZ |  |  | $45 |  |  |  | $118 |  |  |  | $192 |  |  |  | $388 |
NKX |  |  | $48 |  |  |  | $124 |  |  |  | $202 |  |  |  | $407 |
NAC |  |  | $48 |  |  |  | $125 |  |  |  | $203 |  |  |  | $409 |
NAN |  |  | $48 |  |  |  | $124 |  |  |  | $202 |  |  |  | $407 |
The example should not be considered a representation of future expenses. Actual expenses may be greater or less than those shown above. |  |  |  |  |  |  |  |
Expense Example, Year 01 |  |  |  |  |  |  |  |  |  |  | $ 45 |  |  |  |  |  |  |  |
Expense Example, Years 1 to 3 |  |  |  |  |  |  |  |  |  |  | 118 |  |  |  |  |  |  |  |
Expense Example, Years 1 to 5 |  |  |  |  |  |  |  |  |  |  | 192 |  |  |  |  |  |  |  |
Expense Example, Years 1 to 10 |  |  |  |  |  |  |  |  |  |  | $ 388 |  |  |  |  |  |  |  |
Purpose of Fee Table , Note [Text Block] |  |  |  |  |  |  |  |  |  |  | The purpose of the tables and the example below are to help you understand all fees and expenses that you, as a common shareholder, would bear directly or indirectly. The tables show the expenses of the Fund as a percentage of the average net assets applicable to Common Shares and not as a percentage of total assets or managed assets. |  |  |  |  |  |  |  |
Basis of Transaction Fees, Note [Text Block] |  |  |  |  |  |  |  |  |  |  | as a percentage of offering price |  |  |  |  |  |  |  |
Other Expenses, Note [Text Block] |  |  |  |  |  |  |  |  |  |  |
(2) | Interest and Other Related Expenses reflect actual expenses and fees for leverage incurred by a Fund for the fiscal year ended August 31, 2025. The types of leverage used by the Fund during the fiscal year ended August 31, 2025 are described in the Fund Leverage and the Notes to Financial Statements sections of this annual report. Actual Interest and Other Related Expenses incurred in the future may be higher or lower. If short-term market interest rates rise in the future, and if the Fund continues to maintain leverage, the cost of which is tied to short-term interest rates, the Fund’s interest expenses on its short-term borrowings can be expected to rise in tandem. The Fund’s use of leverage will increase the amount of management fees paid to the Fund’s adviser and sub-advisor(s).
(3) | Other Expenses are based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%.
Financial Highlights [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Securities [Table Text Block] |  |  |  |  |  |  |  |  |  |  | The following table sets forth information regarding each Fund’s outstanding senior securities as of the end of each of the Fund’s last ten fiscal years, as applicable. Each Fund’s senior securities during this time period are comprised of borrowings that constitute “senior securities” as defined in the Investment Company Act of 1940, as amended (1940 Act). The information in this table is derived from the financial statements. The financial statements for the year ended August 31, 2025 have been audited by PricewaterhouseCoopers LLP (“PwC”), independent registered public accounting firm. The financial statements with respect to the fiscal years ended prior to 2025, where applicable, have been audited by other auditors. The Funds’ audited financial statements for the year ended August 31, 2025, including the report of PwC thereon, and accompanying notes thereto, are included in this Annual Report.
NAZ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  | Adjustable Rate MuniFund Term Preferred (AMTP) Shares at the End of Period |  |  | Variable Rate MuniFund Term Preferred (VMTP) Shares at the End of Period |
|  | Aggregate Amount Outstanding (000) (1) |  |  | Asset Coverage Per $100,000 (3) |  |  | Aggregate Amount Outstanding (000) (1) |  |  | Asset Coverage Per $100,000 (3) |
2025 |  |  | $ 88,300 |  |  |  | $ 252,413 |  |  |  | $ 0 |  |  |  | $ 0 |
2024 (5) |  |  | $ 88,300 |  |  |  | $ 265,542 |  |  |  | $ 0 |  |  |  | $ 0 |
2024 |  |  | $ 88,300 |  |  |  | $ 266,396 |  |  |  | $ 0 |  |  |  | $ 0 |
2023 |  |  | $ 88,300 |  |  |  | $ 261,963 |  |  |  | $ 0 |  |  |  | $ 0 |
2022 |  |  | $ 88,300 |  |  |  | $ 290,229 |  |  |  | $ 0 |  |  |  | $ 0 |
2021 |  |  | $ 88,300 |  |  |  | $ 297,509 |  |  |  | $ 0 |  |  |  | $ 0 |
2020 |  |  | $ 88,300 |  |  |  | $ 303,878 |  |  |  | $ 0 |  |  |  | $ 0 |
2019 |  |  | $ 88,300 |  |  |  | $ 285,822 |  |  |  | $ 0 |  |  |  | $ 0 |
2018 |  |  | $ 0 |  |  |  | $ 0 |  |  |  | $ 88,300 |  |  |  | $ 286,891 |
2017 |  |  | $ 0 |  |  |  | $ 0 |  |  |  | $ 88,300 |  |  |  | $ 287,022 |
2016 |  |  | $ 0 |  |  |  | $ 0 |  |  |  | $ 79,000 |  |  |  | $ 319,959 |
(1) | Aggregate Amount Outstanding: Aggregate amount outstanding represents the principal amount outstanding or liquidation preference, if applicable, as of the end of the relevant fiscal year and does not include any preferred shares noticed for redemption as noted on the Statement of Assets and Liabilities, if applicable.
(3) | Asset Coverage Per $100,000: Asset coverage per $100,000 is calculated by subtracting the Fund’s liabilities and indebtedness not represented by senior securities from the Fund’s total assets, dividing the result by the aggregate of the involuntary liquidation preference of the outstanding preferred shares and multiplying the result by 100,000. For purpose of asset coverage above, senior securities consist of preferred shares or borrowings (excluding temporary borrowings) of a Fund and does not include derivative transactions and other investments that have the economic effect of leverage such as reverse repurchase agreements and tender option bonds. If the leverage effects of such investments were included, the asset coverage amounts presented would be lower.
(5) | For the six months ended August 31, 2024. Prior to March 1, 2024, the Fund’s fiscal year end was February 29th.
Senior Securities, Note [Text Block] |  |  |  |  |  |  |  |  |  |  | SENIOR SECURITIES The following table sets forth information regarding each Fund’s outstanding senior securities as of the end of each of the Fund’s last ten fiscal years, as applicable. Each Fund’s senior securities during this time period are comprised of borrowings that constitute “senior securities” as defined in the Investment Company Act of 1940, as amended (1940 Act). The information in this table is derived from the financial statements. The financial statements for the year ended August 31, 2025 have been audited by PricewaterhouseCoopers LLP (“PwC”), independent registered public accounting firm. The financial statements with respect to the fiscal years ended prior to 2025, where applicable, have been audited by other auditors. The Funds’ audited financial statements for the year ended August 31, 2025, including the report of PwC thereon, and accompanying notes thereto, are included in this Annual Report.
NAZ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
|  | Adjustable Rate MuniFund Term Preferred (AMTP) Shares at the End of Period |  |  | Variable Rate MuniFund Term Preferred (VMTP) Shares at the End of Period |
|  | Aggregate Amount Outstanding (000) (1) |  |  | Asset Coverage Per $100,000 (3) |  |  | Aggregate Amount Outstanding (000) (1) |  |  | Asset Coverage Per $100,000 (3) |
2025 |  |  | $ 88,300 |  |  |  | $ 252,413 |  |  |  | $ 0 |  |  |  | $ 0 |
2024 (5) |  |  | $ 88,300 |  |  |  | $ 265,542 |  |  |  | $ 0 |  |  |  | $ 0 |
2024 |  |  | $ 88,300 |  |  |  | $ 266,396 |  |  |  | $ 0 |  |  |  | $ 0 |
2023 |  |  | $ 88,300 |  |  |  | $ 261,963 |  |  |  | $ 0 |  |  |  | $ 0 |
2022 |  |  | $ 88,300 |  |  |  | $ 290,229 |  |  |  | $ 0 |  |  |  | $ 0 |
2021 |  |  | $ 88,300 |  |  |  | $ 297,509 |  |  |  | $ 0 |  |  |  | $ 0 |
2020 |  |  | $ 88,300 |  |  |  | $ 303,878 |  |  |  | $ 0 |  |  |  | $ 0 |
2019 |  |  | $ 88,300 |  |  |  | $ 285,822 |  |  |  | $ 0 |  |  |  | $ 0 |
2018 |  |  | $ 0 |  |  |  | $ 0 |  |  |  | $ 88,300 |  |  |  | $ 286,891 |
2017 |  |  | $ 0 |  |  |  | $ 0 |  |  |  | $ 88,300 |  |  |  | $ 287,022 |
2016 |  |  | $ 0 |  |  |  | $ 0 |  |  |  | $ 79,000 |  |  |  | $ 319,959 |
(1) | Aggregate Amount Outstanding: Aggregate amount outstanding represents the principal amount outstanding or liquidation preference, if applicable, as of the end of the relevant fiscal year and does not include any preferred shares noticed for redemption as noted on the Statement of Assets and Liabilities, if applicable.
(3) | Asset Coverage Per $100,000: Asset coverage per $100,000 is calculated by subtracting the Fund’s liabilities and indebtedness not represented by senior securities from the Fund’s total assets, dividing the result by the aggregate of the involuntary liquidation preference of the outstanding preferred shares and multiplying the result by 100,000. For purpose of asset coverage above, senior securities consist of preferred shares or borrowings (excluding temporary borrowings) of a Fund and does not include derivative transactions and other investments that have the economic effect of leverage such as reverse repurchase agreements and tender option bonds. If the leverage effects of such investments were included, the asset coverage amounts presented would be lower.
(5) | For the six months ended August 31, 2024. Prior to March 1, 2024, the Fund’s fiscal year end was February 29th.
Senior Securities Headings, Note [Text Block] |  |  |  |  |  |  |  |  |  |  | The following table sets forth information regarding each Fund’s outstanding senior securities as of the end of each of the Fund’s last ten fiscal years, as applicable. Each Fund’s senior securities during this time period are comprised of borrowings that constitute “senior securities” as defined in the Investment Company Act of 1940, as amended (1940 Act). The information in this table is derived from the financial statements. The financial statements for the year ended August 31, 2025 have been audited by PricewaterhouseCoopers LLP (“PwC”), independent registered public accounting firm. The financial statements with respect to the fiscal years ended prior to 2025, where applicable, have been audited by other auditors. The Funds’ audited financial statements for the year ended August 31, 2025, including the report of PwC thereon, and accompanying notes thereto, are included in this Annual Report. |  |  |  |  |  |  |  |
Senior Securities Highlights Audited, Note [Text Block] |  |  |  |  |  |  |  |  |  |  | The information in this table is derived from the financial statements. The financial statements for the year ended August 31, 2025 have been audited by PricewaterhouseCoopers LLP (“PwC”), independent registered public accounting firm. The financial statements with respect to the fiscal years ended prior to 2025, where applicable, have been audited by other auditors. The Funds’ audited financial statements for the year ended August 31, 2025, including the report of PwC thereon, and accompanying notes thereto, are included in this Annual Report. |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment Objectives and Practices [Text Block] |  |  |  |  |  |  |  |  |  |  | Investment Objectives The Fund’s primary investment objective is current income exempt from both regular federal income taxes and Arizona individual income taxes, and its secondary investment objective is the enhancement of portfolio value relative to the Arizona municipal bond market through investments in tax-exempt Arizona Municipal Obligations (as defined below) that, in the opinion of the Fund’s investment adviser, are underrated or undervalued or that represent municipal market sectors that are undervalued. Investment Policies As a fundamental policy, under normal circumstances, the Fund will invest at least 80% of its Assets (as defined below) in municipal securities and other related investments the income from which is exempt from regular federal and Arizona income taxes. “Assets” mean the net assets of the Fund plus the amount of any borrowings for investment purposes. “Managed Assets” mean the total assets of the Fund, minus the sum of its accrued liabilities (other than Fund liabilities incurred for the express purpose of creating leverage). Total assets for this purpose shall include assets attributable to the Fund’s use of leverage (whether or not those assets are reflected in the Fund’s financial statements for purposes of generally accepted accounting principles), and derivatives will be valued at their market value. Under normal circumstances:
| ● |  | The Fund will invest at least 80% of its Managed Assets in investment grade securities that, at the time of investment, are rated within the four highest grades (Baa or BBB or better) by at least one nationally recognized statistical rating organization (“NRSRO”) or are unrated but judged to be of comparable quality by the Fund’s sub-adviser.
| ● |  | The Fund may invest up to 20% of its Managed Assets in municipal securities that at the time of investment are rated below investment grade or are unrated but judged to be of comparable quality by the Fund’s sub-adviser.
| ● |  | No more than 10% of the Fund’s Managed Assets may be invested in municipal securities rated below B3/B- or that are unrated but judged to be of comparable quality by the Fund’s sub-adviser.
| ● |  | The Fund may invest up to 20% of its Managed Assets in municipal securities that pay interest that is taxable under the federal alternative minimum tax.
| ● |  | The Fund may invest up to 15% of its Managed Assets in inverse floating rate securities.
| ● |  | The Fund will generally maintain an investment portfolio with an overall weighted average maturity of greater than 10 years.
The foregoing policies apply only at the time of any new investment. Approving Changes in Investment Policies The Board of Trustees of the Fund may change the policies described above without a shareholder vote. However, the Fund’s (i) investment objectives, (ii) policy of investing at least 80% of its Assets in municipal securities and other related investments the income from which is exempt from regular federal and Arizona income taxes, (iii) policy (as described below) that it may not issue debt securities that rank senior to Preferred Shares (as defined below) other than for temporary or emergency purposes and (iv) policy (as described below) that it may not borrow money, except from banks for temporary or emergency purposes, or to repurchase its shares, subject to certain restrictions, may not be changed without the approval of the holders of a majority of the outstanding common shares and preferred shares voting together as a single class, and the approval of the holders of a majority of the outstanding preferred shares, voting separately as a single class. A “majority of the outstanding” shares means (i) 67% or more of the shares present at a meeting, if the holders of more than 50% of the shares are present or represented by proxy or (ii) more than 50% of the shares, whichever is less. Portfolio Contents The Fund invests in various municipal securities, including municipal bonds and notes, other securities issued to finance and refinance public projects, and other related securities and derivative instruments creating exposure to municipal bonds, notes and securities that provide for the payment of interest income that is exempt from federal and Arizona income tax (for purposes of the Fund’s investment objectives, “Arizona Municipal Obligations”). The Fund generally invests in municipal securities. Municipal securities include municipal bonds, notes, securities issued to finance and refinance public projects, certificates of participation, variable rate demand obligations, lease obligations, municipal notes, pre-refunded municipal bonds, private activity bonds, securities issued by tender option bond trusts (“TOB trusts”), including inverse floating rate securities, and other forms of municipal bonds and securities, and other related instruments that create exposure to municipal bonds, notes and securities that provide for the payment of interest income that is exempt from regular U.S. federal income tax and Arizona income taxes. Municipal securities are debt obligations generally issued by states, cities and local authorities and certain possessions and territories of the United States (such as Puerto Rico and Guam) to finance or refinance public purpose projects such as roads, schools, and water supply systems. The Fund may also invest in municipal securities that pay interest that is taxable under the federal alternative minimum tax applicable to noncorporate taxpayers (“AMT Bonds”). AMT Bonds may trigger adverse tax consequences for Fund shareholders who are subject to the federal alternative minimum tax. The municipal securities in which the Fund invests are generally issued by the State of Arizona, a municipality of Arizona, or a political subdivision of either, and pay interest that, in the opinion of bond counsel to the issuer (or on the basis of other authority believed by the Fund’s sub-adviser to be reliable), is exempt from regular federal and Arizona income taxes, although the interest may be subject to the federal alternative minimum tax. The Fund may invest in municipal securities issued by U.S. territories (such as Puerto Rico or Guam) that are exempt from regular federal and Arizona income taxes. The Fund may invest in municipal securities that represent lease obligations and certificates of participation in such leases. A municipal lease is an obligation in the form of a lease or installment purchase that is issued by a state or local government to acquire equipment and facilities. Income from such obligations generally is exempt from state and local taxes in the state of issuance. A certificate of participation represents an undivided interest in an unmanaged pool of municipal leases, an installment purchase agreement or other instruments. The certificates typically are issued by a municipal agency, a trust or other entity that has received an assignment of the payments to be made by the state or political subdivision under such leases or installment purchase agreements. Such certificates provide the Fund with the right to a pro rata undivided interest in the underlying municipal securities. In addition, such participations generally provide the Fund with the right to demand payment, on not more than seven days’ notice, of all or any part of the Fund’s participation interest in the underlying municipal securities, plus accrued interest. The Fund may invest in municipal notes. Municipal securities in the form of notes generally are used to provide for short-term capital needs, in anticipation of an issuer’s receipt of other revenues or financing, and typically have maturities of up to three years. Such instruments may include tax anticipation notes, revenue anticipation notes, bond anticipation notes, tax and revenue anticipation notes and construction loan notes. Tax anticipation notes are issued to finance the working capital needs of governments. Generally, they are issued in anticipation of various tax revenues, such as income, sales, property, use and business taxes, and are payable from these specific future taxes. Revenue anticipation notes are issued in expectation of receipt of other kinds of revenue, such as federal revenues available under federal revenue sharing programs. Bond anticipation notes are issued to provide interim financing until long-term bond financing can be arranged. In most cases, the long-term bonds then provide the funds needed for repayment of the bond anticipation notes. Tax and revenue anticipation notes combine the funding sources of both tax anticipation notes and revenue anticipation notes. Construction loan notes are sold to provide construction financing. Mortgage notes insured by the Federal Housing Authority secure these notes; however, the proceeds from the insurance may be less than the economic equivalent of the payment of principal and interest on the mortgage note if there has been a default. The anticipated revenues from taxes, grants or bond financing generally secure the obligations of an issuer of municipal notes. The Fund may invest in “tobacco settlement bonds.” Tobacco settlement bonds are municipal securities that are secured or payable solely from the collateralization of the proceeds from class action or other litigation against the tobacco industry. The Fund may invest in pre-refunded municipal securities. The principal of and interest on pre-refunded municipal securities are no longer paid from the original revenue source for the securities. Instead, the source of such payments is typically an escrow fund consisting of U.S. government securities. The assets in the escrow fund are derived from the proceeds of refunding bonds issued by the same issuer as the pre-refunded municipal securities. Issuers of municipal securities use this advance refunding technique to obtain more favorable terms with respect to securities that are not yet subject to call or redemption by the issuer. For example, advance refunding enables an issuer to refinance debt at lower market interest rates, restructure debt to improve cash flow or eliminate restrictive covenants in the indenture or other governing instrument for the pre-refunded municipal securities. However, except for a change in the revenue source from which principal and interest payments are made, the pre- refunded municipal securities remain outstanding on their original terms until they mature or are redeemed by the issuer. The Fund may invest in private activity bonds. Private activity bonds are issued by or on behalf of public authorities to obtain funds to provide privately operated housing facilities, airport, mass transit or port facilities, sewage disposal, solid waste disposal or hazardous waste treatment or disposal facilities and certain local facilities for water supply, gas or electricity. Other types of private activity bonds, the proceeds of which are used for the construction, equipment, repair or improvement of privately operated industrial or commercial facilities, may constitute municipal securities, although the current federal tax laws place substantial limitations on the size of such issues. The Fund may invest in inverse floating rate securities issued by a TOB trust, the interest rate on which varies inversely with the Securities Industry Financial Markets Association short-term rate, which resets weekly, or a similar short-term rate, and is reduced by the expenses related to the TOB trust. Typically, inverse floating rate securities represent beneficial interests in a special purpose trust (sometimes called a TOB trust) formed by a third party sponsor for the purpose of holding municipal bonds. Inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate on the municipal bond held by the TOB trust, which effectively leverages the Fund’s investment. The Fund may invest in floating rate securities issued by special purpose trusts. Floating rate securities may take the form of short-term floating rate securities or the option period may be substantially longer. Generally, the interest rate earned will be based upon the market rates for municipal securities with maturities or remarketing provisions that are comparable in duration to the periodic interval of the tender option, which may vary from weekly, to monthly, to extended periods of one year or multiple years. Since the option feature has a shorter term than the final maturity or first call date of the underlying bond deposited in the trust, the Fund as the holder of the floating rate security relies upon the terms of the agreement with the financial institution furnishing the option as well as the credit strength of that institution. As further assurance of liquidity, the terms of the trust provide for a liquidation of the municipal security deposited in the trust and the application of the proceeds to pay off the floating rate security. The trusts that are organized to issue both short-term floating rate securities and inverse floaters generally include liquidation triggers to protect the investor in the floating rate security. The Fund may invest in municipal securities issued by special taxing districts. Special taxing districts are organized to plan and finance infrastructure developments to induce residential, commercial and industrial growth and redevelopment. The bond financing methods such as tax increment finance, tax assessment, special services district and Mello-Roos bonds, are generally payable solely from taxes or other revenues attributable to the specific projects financed by the bonds without recourse to the credit or taxing power of related or overlapping municipalities. The Fund may invest in zero coupon bonds. A zero coupon bond is a bond that typically does not pay interest for the entire life of the obligation or for an initial period after the issuance of the obligation. The Fund may buy and sell securities on a when-issued or delayed delivery basis, making payment or taking delivery at a later date, normally within 15 to 45 days of the trade date. The Fund may utilize structured notes and similar instruments for investment purposes and also for hedging purposes. Structured notes are privately negotiated debt obligations where the principal and/or interest is determined by reference to the performance of a benchmark asset, market or interest rate (an “embedded index”), such as selected securities, an index of securities or specified interest rates, or the differential performance of two assets or markets. The Fund may invest in illiquid securities (i.e., securities that are not readily marketable), including, but not limited to, restricted securities (securities the disposition of which is restricted under the federal securities laws), securities that may be resold only pursuant to Rule 144A under the Securities Act of 1933, as amended (the “1933 Act”), and repurchase agreements with maturities in excess of seven days. Illiquid securities may also include securities legally restricted as to resale, such as securities issued pursuant to Section 4(a)(2) of the 1933 Act. The Fund may enter into certain derivative instruments in pursuit of its investment objectives, including to seek to enhance return, to hedge certain risks of its investments in municipal securities or as a substitute for a position in the underlying asset. Such instruments include financial futures contracts, swap contracts (including interest rate swaps, credit default swaps and municipal market data rate locks (“MMD Rate Locks”)), options on financial futures, options on swap contracts or other derivative instruments. The Fund may purchase and sell MMD Rate Locks. An MMD Rate Lock permits the Fund to lock in a specified municipal interest rate for a portion of its portfolio to preserve a return on a particular investment or a portion of its portfolio as a duration management technique or to protect against any increase in the price of securities to be purchased at a later date. By using an MMD Rate Lock, the Fund can create a synthetic long or short position, allowing the Fund to select what the manager believes is an attractive part of the yield curve. The Fund will ordinarily use these transactions as a hedge or for duration or risk management although it is permitted to enter into them to enhance income or gain or to increase the Fund’s yield, for example, during periods of steep interest rate yield curves (i.e., wide differences between short term and long-term interest rates). The Fund may also invest in securities of other open- or closed-end investment companies (including exchange traded funds (“ETFs”)) that invest primarily in municipal securities of the types in which the Fund may invest directly, to the extent permitted by the Investment Company Act of 1940, as amended (the “1940 Act”), the rules and regulations issued thereunder and applicable exemptive orders issued by the Securities and Exchange Commission (“SEC”). The Fund may invest in distressed securities but may not invest in the securities of an issuer which, at the time of investment, is in default on its obligations to pay principal or interest thereon when due or that is involved in a bankruptcy proceeding (i.e., rated below C-, at the time of investment); provided, however, that the Fund’s sub-adviser may determine that it is in the best interest of shareholders in pursuing a workout arrangement with issuers of defaulted securities to make loans to the defaulted issuer or another party, or purchase a debt, equity or other interest from the defaulted issuer or another party, or take other related or similar steps involving the investment of additional monies, but only if that issuer’s securities are already held by the Fund. Use of Leverage The Fund uses leverage to pursue its investment objectives. The Fund may source leverage through the issuance of “senior securities” as defined under the 1940 Act, which include the issuance of preferred shares of beneficial interest (“Preferred Shares”) and borrowings, except that the Fund may not issue debt securities. However, the Fund’s use of borrowings (which may include reverse repurchase agreements) for leverage is limited by certain fundamental investment restrictions. Additionally, the Fund may use certain derivatives and other financing instruments that have the economic effect of leverage by creating additional investment exposures, such as investments in inverse floating rate securities. The amount and sources of leverage will vary depending on market conditions. Temporary Defensive Periods During temporary defensive periods (e.g., times when, in the Fund’s investment adviser’s and/or the Fund’s sub-adviser’s opinion, temporary imbalances of supply and demand or other temporary dislocations in the tax-exempt bond market adversely affect the price at which long-term or intermediate-term municipal securities are available), the Fund may invest up to 100% of its net assets in cash or cash equivalents, short-term investments or municipal bonds and deviate from its investment policies including the Fund’s 80% names rule policy. Also, during these periods, the Fund may not achieve its investment objectives. |  |  |  |  |  |  |  |
Risk Factors [Table Text Block] |  |  |  |  |  |  |  |  |  |  | PRINCIPAL RISKS OF THE FUNDS The factors that are most likely to have a material effect on a particular Fund’s portfolio as a whole are called “principal risks.” Each Fund is subject to the principal risks indicated below, whether through direct investment or derivative positions. Each Fund may be subject to additional risks other than those identified and described below because the types of investments made by a Fund can change over time.
Risk |  | NAZ |  | NKX |  | NCA |  | NAC |  | NXJ |  | NRK |  | NNY |  | NAN |  | NQP
Portfolio Level Risks |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Alternative Minimum Tax Risk |  | X |  | - |  | X |  | X |  | X |  | - |  | X |  | X |  | X
Below Investment Grade Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Call Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Credit Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Credit Spread Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Deflation Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Derivatives Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Distressed or Defaulted Securities Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Duration Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Economic Sector Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Floating and Variable Rate Securities Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Financial Futures and Options Transactions Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Hedging Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Income Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Inflation Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Insurance Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Interest Rate Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Inverse Floating Rate Securities Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Municipal Securities Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Municipal Securities Market Liquidity Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Municipal Securities Market Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Other Investment Companies Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Puerto Rico Municipal Securities Market Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Reinvestment Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Restricted and Illiquid Investments Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Special Considerations Related to Single State Concentration Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Special Risks Related to Certain Municipal Obligations |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Structured Products Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Swap Transactions Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Tax Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Taxability Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Tobacco Settlement Bond Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Unrated Securities Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Valuation Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
When-Issued and Delayed-Delivery Transactions Risks |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Zero Coupon Bonds Risk or Pay-In-Kind Securities Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Risk |  | NAZ |  | NKX |  | NCA |  | NAC |  | NXJ |  | NRK |  | NNY |  | NAN |  | NQP
Fund Level and Other Risks |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Anti-Takeover Provisions Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Counterparty Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Cybersecurity Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Economic and Political Events Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Fund Tax Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Global Economic Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Investment and Market Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Legislation and Regulatory Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Leverage Risk |  | X |  | X |  | - |  | X |  | X |  | X |  | - |  | X |  | X
Market Discount from Net Asset Value |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Recent Market Conditions |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Reverse Repurchase Agreement Risk |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X |  | X
Portfolio Level Risks: Alternative Minimum Tax Risk. As a result of the Fund’s investments in AMT Bonds, a portion of the Fund’s otherwise exempt-interest dividends may be taxable to those shareholders subject to the federal alternative minimum tax. Below Investment Grade Risk. Municipal securities of below investment grade quality are regarded as having speculative characteristics with respect to the issuer’s capacity to pay dividends or interest and repay principal, and may be subject to higher price volatility and default risk than investment grade municipal securities of comparable terms and duration. Issuers of lower grade municipal securities may be highly leveraged and may not have available to them more traditional methods of financing. The prices of these lower grade securities are typically more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn. The secondary market for lower rated municipal securities may not be as liquid as the secondary market for more highly rated municipal securities, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular municipal security. If a below investment grade municipal security goes into default, or its issuer enters bankruptcy, it might be difficult to sell that security in a timely manner at a reasonable price. Call Risk. The Fund may invest in municipal securities that are subject to call risk. Such municipal securities may be redeemed at the option of the issuer, or “called,” before their stated maturity or redemption date. In general, an issuer will call its instruments if they can be refinanced by issuing new instruments that bear a lower interest rate. The Fund is subject to the possibility that during periods of falling interest rates, an issuer will call its high yielding municipal securities. The Fund would then be forced to invest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund’s income. Credit Risk. Issuers of municipal securities in which the Fund may invest may default on their obligations, including to pay principal or interest when due. This non-payment would result in a reduction of income to the Fund, a reduction in the value of a municipal security experiencing non-payment and potentially a decrease in the net asset value (“NAV”) of the Fund. To the extent that the credit rating assigned to a municipal security in the Fund’s portfolio is downgraded, the market price and liquidity of such security may be adversely affected. Credit Spread Risk. Credit spread risk is the risk that credit spreads (i.e., the difference in yield between securities that is due to differences in their credit quality) may increase when the market believes that municipal securities generally have a greater risk of default. Increasing credit spreads may reduce the market values of the Fund’s securities. Credit spreads often increase more for lower rated and unrated securities than for investment grade securities. In addition, when credit spreads increase, reductions in market value will generally be greater for longer-maturity securities. Deflation Risk. Deflation risk is the risk that prices throughout the economy decline over time. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. Derivatives Risk. The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a municipal security or other asset without buying or selling the municipal security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over-the-counter derivative transaction between the Fund and a counterparty that is not cleared through a central counterparty also involves the risk that a loss may be sustained as a result of the failure of the counterparty to the contract to make required payments. The payment obligation for a cleared derivative transaction is guaranteed by a central counterparty, which exposes the Fund to the creditworthiness of the central counterparty. The use of certain derivatives involves leverage, which can cause the Fund’s portfolio to be more volatile than if the portfolio had not been leveraged. Leverage can significantly magnify the effect of price movements of the reference asset, disproportionately increasing the Fund’s losses and reducing the Fund’s opportunities for gains when the reference asset changes in unexpected ways. In some instances, such leverage could result in losses that exceed the original amount invested. It is possible that regulatory or other developments in the derivatives market, including changes in government regulation, could adversely impact the Fund’s ability to invest in certain derivatives or successfully use derivative instruments. Distressed or Defaulted Securities Risk. Investments in “distressed” securities, meaning those whose issuers are experiencing financial difficulties or distress at the time the security is acquired, present a substantial risk of future default. In the event distressed securities become defaulted securities or the Fund otherwise holds defaulted securities, the Fund may incur losses, including additional expenses, to the extent it is required to seek recovery upon a default in the payment of principal or interest on those investments. In any reorganization or liquidation proceeding relating to a portfolio investment, the Fund may lose its entire investment or may be required to accept cash or securities with a value less than its original investment. Defaulted or distressed securities may be subject to restrictions on resale. Duration Risk. Duration is the sensitivity, expressed in years, of the price of a fixed-income security to changes in the general level of interest rates (or yields). Securities with longer durations tend to be more sensitive to interest rate (or yield) changes, which typically corresponds to increased volatility and risk, than securities with shorter durations. For example, if a security or portfolio has a duration of three years and interest rates increase by 1%, then the security or portfolio would decline in value by approximately 3%. Duration differs from maturity in that it considers potential changes to interest rates, and a security’s coupon payments, yield, price and par value and call features, in addition to the amount of time until the security matures. The duration of a security will be expected to change over time with changes in market factors and time to maturity. Economic Sector Risk. The Fund may invest a significant amount of its total assets in municipal securities in the same economic sector. This may make the Fund more susceptible to adverse economic, political or regulatory occurrences affecting an economic sector, making the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. As the percentage of the Fund’s Managed Assets invested in a particular sector increases, so does the potential for fluctuation in the value of the Fund’s assets. In addition, the Fund may invest a significant portion of its assets in certain sectors of the municipal securities market, such as health care facilities, private educational facilities, special taxing districts and start-up utility districts, and private activity bonds including industrial development bonds on behalf of transportation companies, whose credit quality and performance may be more susceptible to economic, business, political, regulatory and other developments than other sectors of municipal issuers. If the Fund invests a significant portion of its assets in one or more particular sectors, the Fund’s performance may be subject to additional risk and variability. Floating and Variable Rate Securities Risk. Floating and variable rate securities provide for adjustment in the interest rate paid on the obligations. The terms of such obligations typically provide that interest rates are adjusted based upon an interest or market rate adjustment as provided in the respective obligations. The adjustment intervals may be regular, and range from daily up to annually, or may be event-based, such as based on a change in the prime rate. Because of the interest rate adjustment feature, floating and variable rate securities provide an investor with a certain degree of protection against rises in interest rates, although the investor will participate in any declines in interest rates as well. Generally, changes in interest rates will have a smaller effect on the market value of floating and variable rate securities than on the market value of comparable fixed-income obligations. Thus, investing in floating and variable rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed-income securities. Floating and variable rate securities may be subject to greater liquidity risk than other debt securities, meaning that there may be limitations on the Fund’s ability to sell the securities at any given time. Such securities also may lose value. Financial Futures and Options Transactions Risk. The Fund may use certain transactions for hedging the portfolio’s exposure to credit risk and the risk of increases in interest rates, which could result in poorer overall performance for the Fund. There may be an imperfect correlation between price movements of the futures and options and price movements of the portfolio securities being hedged. If the Fund engages in futures transactions or in the writing of options on futures, it will be required to maintain initial margin and maintenance margin and may be required to make daily variation margin payments in accordance with applicable rules of the exchanges and the Commodity Futures Trading Commission (“CFTC”). If the Fund purchases a financial futures contract or a call option or writes a put option in order to hedge the anticipated purchase of municipal securities, and if the Fund fails to complete the anticipated purchase transaction, the Fund may have a loss or a gain on the futures or options transaction that will not be offset by price movements in the municipal securities that were the subject of the anticipatory hedge. There can be no assurance that a liquid market will exist at a time when the Fund seeks to close out a derivatives or futures or a futures option position, and the Fund would remain obligated to meet margin requirements until the position is closed. Hedging Risk. The Fund’s use of derivatives or other transactions to reduce risk involves costs and will be subject to the investment adviser’s and/or the sub-adviser’s ability to predict correctly changes in the relationships of such hedge instruments to the Fund’s portfolio holdings or other factors. No assurance can be given that the investment adviser’s and/or the sub-adviser’s judgment in this respect will be correct, and no assurance can be given that the Fund will enter into hedging or other transactions at times or under circumstances in which it may be advisable to do so. Hedging activities may reduce the Fund’s opportunities for gain by offsetting the positive effects of favorable price movements and may result in net losses. Income Risk. The Fund’s level of current income could decline due to falling market interest rates. This is because, in a falling interest rate environment, the Fund generally will have to invest the proceeds from maturing portfolio securities in lower-yielding securities. Inflation Risk. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the common shares and distributions can decline. Currently, inflation rates are elevated relative to normal market conditions and could increase. Insurance Risk. The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub-prime mortgages and other lower credit quality investments. As a result, such losses reduced the insurers’ capital and called into question their continued ability to perform their obligations under such insurance if they are called upon to do so in the future. While an insured municipal security will typically be deemed to have the rating of its insurer, if the insurer of a municipal security suffers a downgrade in its credit rating or the market discounts the value of the insurance provided by the insurer, the value of the municipal security would more closely, if not entirely, reflect such rating. In such a case, the value of insurance associated with a municipal security may not add any value. The insurance feature of a municipal security does not guarantee the full payment of principal and interest through the life of an insured obligation, the market value of the insured obligation or the NAV of the common shares represented by such insured obligation. Interest Rate Risk. Interest rate risk is the risk that municipal securities in the Fund’s portfolio will decline in value because of changes in market interest rates. Generally, when market interest rates rise, the market value of such securities will fall, and vice versa. As interest rates decline, issuers of municipal securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower-yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower than expected principal payments may extend the average life of municipal securities, potentially locking in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer- term municipal securities generally fluctuate more than prices of shorter-term municipal securities as interest rates change. If the Fund invests in floating rate securities, the market value of such securities may fall in a declining interest rate environment and may also fall in a rising interest rate environment if there is a lag between the rise in interest rates and the reset. A secondary risk associated with declining interest rates is the risk that income earned by the Fund on floating rate securities may decline due to lower coupon payments on floating-rate securities. Inverse Floating Rate Securities Risk. In general, income on inverse floating rate securities will decrease when short-term interest rates increase and increase when short-term interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal. In addition, inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of fixed rate securities. The Fund may invest in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities. The Fund may be required to sell its inverse floating rate securities at less than favorable prices, or liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following:
| • |  | If the Fund has a need for cash and the securities in a special purpose trust are not actively trading due to adverse market conditions;
| • |  | If special purpose trust sponsors (as a collective group or individually) experience financial hardship and consequently seek to terminate their respective outstanding special purpose trusts; and
| • |  | If the value of an underlying security declines significantly and if additional collateral has not been posted by the Fund.
Municipal Securities Risk. The values of municipal securities may be adversely affected by local political and economic conditions and developments. Adverse conditions in an industry significant to a local economy could have a correspondingly adverse effect on the financial condition of local issuers. Other factors that could affect municipal securities include a change in the local, state, or national economy, a downgrade of a state’s credit rating or the rating of authorities or political subdivisions of the state, demographic factors, ecological or environmental concerns, inability or perceived inability of a government authority to collect sufficient tax or other revenues, statutory limitations on the issuer’s ability to increase taxes, and other developments generally affecting the revenue of issuers (for example, legislation or court decisions reducing state aid to local governments or mandating additional services). This risk would be heightened to the extent that the Fund invests a substantial portion of the below-investment grade quality portion of its portfolio in the bonds of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), in industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, municipal lease obligations, private activity bonds or moral obligation bonds) that are particularly exposed to specific types of adverse economic, business or political events. The value of municipal securities may also be adversely affected by rising health care costs, increasing unfunded pension liabilities, and by the phasing out of federal programs providing financial support. In recent periods, a number of municipal issuers have defaulted on obligations, been downgraded or commenced insolvency proceedings. Financial difficulties of municipal issuers may continue or get worse. In addition, the amount of public information available about municipal bonds is generally less than for certain corporate equities or bonds, meaning that the investment performance of the Fund may be more dependent on the analytical abilities of the Fund’s sub‑adviser than funds that invest in stock or other corporate investments. To the extent that a fund invests a significant portion of its assets in the securities of issuers located in a given state or U.S. territory, it will be disproportionally affected by political and economic conditions and developments in that state or territory and may involve greater risk than funds that invest in a larger universe of securities. In addition, economic, political or regulatory changes in that state or territory could adversely affect municipal securities issuers in that state or territory and therefore the value of a fund’s investment portfolio. Municipal Securities Market Liquidity Risk. Inventories of municipal securities held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell municipal securities at attractive prices, and increase municipal security price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of municipal securities to raise cash to meet its obligations, those sales could further reduce the municipal securities’ prices and hurt performance. Municipal Securities Market Risk. The amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the investment performance of the Fund may therefore be more dependent on the analytical abilities of the sub-adviser than if the Fund were a stock fund or taxable bond fund. The secondary market for municipal securities, particularly below investment grade municipal securities, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices. Other Investment Companies Risk. Investing in an investment company exposes the Fund to all of the risks of that investment company’s investments. The Fund, as a holder of the securities of other investment companies, will bear its pro rata portion of the other investment companies’ expenses, including advisory fees. These expenses are in addition to the direct expenses of the Fund’s own operations. As a result, the cost of investing in investment company shares may exceed the costs of investing directly in its underlying investments. In addition, securities of other investment companies may be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities and therefore magnify the Fund’s leverage risk. With respect to ETF’s, an ETF that is based on a specific index may not be able to replicate and maintain exactly the composition and relative weighting of securities in the index. The value of an ETF based on a specific index is subject to change as the values of its respective component assets fluctuate according to market volatility. ETFs typically rely on a limited pool of authorized participants to create and redeem shares, and an active trading market for ETF shares may not develop or be maintained. The market value of shares of ETFs and closed-end funds may differ from their NAV. Puerto Rico Municipal Securities Market Risk. To the extent that the Fund invests a significant portion of its assets in the securities issued by the Commonwealth of Puerto Rico or its political subdivisions, agencies, instrumentalities, or public corporations (collectively referred to as “Puerto Rico” or the “Commonwealth”), it will be disproportionally affected by political, social and economic conditions and developments in the Commonwealth. In addition, economic, political or regulatory changes in that territory could adversely affect the value of the Fund’s investment portfolio. Puerto Rico currently is experiencing significant fiscal and economic challenges, including substantial debt service obligations, high levels of unemployment, underfunded public retirement systems, and persistent government budget deficits. These challenges may negatively affect the value of the Fund’s investments in Puerto Rican municipal securities. Several major ratings agencies have downgraded the general obligation debt of Puerto Rico to below investment grade and continue to maintain a negative outlook for this debt, which increases the likelihood that the rating will be lowered further. In both August 2015 and January 2016, Puerto Rico defaulted on its debt by failing to make full payment due on its outstanding bonds, and there can be no assurance that Puerto Rico will be able to satisfy its future debt obligations. Further downgrades or defaults may place additional strain on the Puerto Rico economy and may negatively affect the value, liquidity, and volatility of the Fund’s investments in Puerto Rican municipal securities. Additionally, numerous issuers have entered Title III of the Puerto Rico Oversite, Management and Economic Stability Act (“PROMESA”), which is similar to bankruptcy protection, through which the Commonwealth of Puerto Rico can restructure its debt. While most of Puerto Rico’s debt has been restructured, proceedings under PROMESA remain ongoing, and it is unclear at this time how those proceedings will be resolved or what impact they will have on the value of the Fund’s investments in Puerto Rico municipal securities. There can be no assurances that these debt restructuring efforts will be effective or that Puerto Rico will be able to service debt payments following the completion of such debt restructuring. In addition, any restructurings approved by a federal court could be appealed and overturned. The mediation process and certain litigation is ongoing with respect to certain municipal securities issued by Puerto Rico and its political subdivisions, instrumentalities and authorities. It is not presently possible to predict the results of this mediation and litigation, but such outcomes will have a significant impact on bondholders of those municipal securities. Further legislation by the U.S. Congress, or actions by the oversight board established by PROMESA, or court approval of an unfavorable debt restructuring deal could have a negative impact on the marketability, liquidity or value of certain investments held by the Fund and could reduce the Fund’s performance. These challenges and uncertainties have been exacerbated by Hurricanes Irma and Maria and the resulting natural disasters in Puerto Rico since 2017. In September 2017, Hurricanes Irma and Maria struck Puerto Rico, causing major damage across the Commonwealth, including damage to its water, power, and telecommunications infrastructure. The length of time needed to rebuild Puerto Rico’s infrastructure is unclear, but could amount to years, during which the commonwealth is likely to be in an uncertain economic state. The full extent of the natural disasters’ impact on Puerto Rico’s economy and foreign investment in Puerto Rico is difficult to estimate. More recently, in late December 2019 and January 2020, a series of earthquakes hit Puerto Rico, including a magnitude 6.4 earthquake, the most powerful earthquake to hit the island in more than a century, causing an estimated $200 million in damage. In addition, in early 2020, as the population of Puerto Rico worked to recover from these natural disasters, the island was significantly impacted by Covid, resulting in the Commonwealth’s authorization of a $787 million relief package to fight the pandemic and its economic impacts. Any reduction in the Commonwealth’s, revenues as a result of the pandemic could have a negative ability on the Commonwealth to meet its debt service obligations, including with respect to debt held by the Fund. Puerto Rico’s political and economic conditions could have a negative impact on the liquidity or value of Puerto Rican municipal securities, and consequently may affect the Fund’s investments and its performance if the Fund invests a significant portion of its assets in Puerto Rican municipal securities. Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called municipal securities at market interest rates that are below the portfolio’s current earnings rate. A decline in income could affect the common shares’ market price, NAV and/or a common shareholder’s overall returns. Restricted and Illiquid Investments Risk. Illiquid investments are investments that are not readily marketable. These investments may include restricted investments, including Rule 144A securities, which cannot be resold to the public without an effective registration statement under the 1933 Act, or, if they are unregistered, may be sold only in a privately negotiated transaction or pursuant to an available exemption from registration. The Fund may not be able to readily dispose of such investments at prices that approximate those at which the Fund could sell such investments if they were more widely traded and, as a result of such illiquidity, the Fund may have to sell other investments or engage in borrowing transactions if necessary to raise cash to meet its obligations. Limited liquidity can also affect the market price of investments, thereby adversely affecting the Fund’s NAV and ability to make dividend distributions. The financial markets in general have in recent years experienced periods of extreme secondary market supply and demand imbalance, resulting in a loss of liquidity during which market prices were suddenly and substantially below traditional measures of intrinsic value. During such periods, some investments could be sold only at arbitrary prices and with substantial losses. Periods of such market dislocation may occur again at any time. Special Considerations Related to Single State Concentration Risk. Because the Fund primarily invests in municipal securities from a single state, the Fund is more susceptible to political, economic or regulatory factors affecting issuers of single state municipal securities. Information regarding the financial condition of the state is ordinarily included in various public documents issued thereby, such as the official statements prepared in connection with the issuance of general obligation bonds for the state. Additionally, the states are party to numerous legal proceedings, many of which normally occur in governmental operations. The creditworthiness of obligations issued by local issuers of the state may be unrelated to the creditworthiness of obligations issued by the state, and that there is no obligation on the part of the state to make payment on such local obligations in the event of default. Special Risks Related to Certain Municipal Obligations. Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non-appropriation” clauses that relieve the governmental issuer of any obligation to make future payments under the lease or contract unless money is appropriated for such purpose by the appropriate legislative body. In addition, such leases or contracts may be subject to the temporary abatement of payments in the event that the governmental issuer is prevented from maintaining occupancy of the leased premises or utilizing the leased equipment. Although the obligations may be secured by the leased equipment or facilities, the disposition of the property in the event of non-appropriation or foreclosure might prove difficult, time consuming and costly, and may result in a delay in recovering or the failure to fully recover the Fund’s original investment. In the event of non-appropriation, the issuer would be in default and taking ownership of the assets may be a remedy available to the Fund, although the Fund does not anticipate that such a remedy would normally be pursued. Certificates of participation involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificates of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation. Structured Products Risk. In addition to the general risks associated with investments in debt securities, holders of structured products bear risks of the underlying investments, index or reference obligation (collectively, the “reference instrument”) and are subject to counterparty, valuation and liquidity risks. The Fund may have the right to receive payments to which it is entitled only from the structured product, and generally does not have direct rights against the issuer or the entity that sold assets to the special purpose trust. While certain structured products enable the investor to acquire interests in a pool of securities without the brokerage and other expenses associated with directly holding the same securities, investors in structured products generally pay their share of the structured product’s administrative and other expenses. When investing in structured products, it is impossible to predict whether the reference instrument will rise or fall, but prices of the reference instrument (and, therefore, the prices of structured products) will be influenced by the same types of political and economic events that affect particular issuers of securities and capital markets generally. Structured products may also be less liquid, more volatile and more difficult to price than other types of securities. Swap Transactions Risk. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by the investment adviser and/or the sub-adviser of not only the referenced asset, rate or index, but also of the swap itself. If the investment adviser and/ or the sub-adviser is incorrect in its forecasts of default risks, market spreads or other applicable factors or events, the investment performance of the Fund would diminish compared with what it would have been if these techniques were not used. Tax Risk. The value of the Fund’s investments and its NAV may be adversely affected by changes in tax rates, rules and policies. Additionally, the Fund is not a suitable investment for individual retirement accounts, for other tax exempt or tax-deferred accounts, for investors who are not sensitive to the federal income tax consequences of their investments. Taxability Risk. The Fund will invest in municipal securities in reliance at the time of purchase on an opinion of bond counsel to the issuer that the interest paid on those securities will be excludable from gross income for regular federal income tax purposes, and the sub-adviser will not independently verify that opinion. Subsequent to the Fund’s acquisition of such a municipal security, however, the security may be determined to pay, or to have paid, taxable income. As a result, the treatment of dividends previously paid or to be paid by the Fund as “exempt-interest dividends” could be adversely affected, subjecting the Fund’s shareholders to increased federal income tax liabilities. Certain other investments made by the Fund, including derivatives transactions, may result in the receipt of taxable income or gains by the Fund. Tobacco Settlement Bond Risk. Tobacco settlement bonds are municipal securities that are backed solely by expected revenues to be derived from lawsuits involving tobacco related deaths and illnesses which were settled between certain states and American tobacco companies. Tobacco settlement bonds are secured by an issuing state’s proportionate share in the Master Settlement Agreement, an agreement between 46 states and nearly all of the U.S. tobacco manufacturers (the “MSA”). Under the terms of the MSA, the actual amount of future settlement payments by tobacco-manufacturers is dependent on many factors, including, among other things, reduced cigarette consumption. Payments made by tobacco manufacturers could be negatively impacted if the decrease in tobacco consumption is significantly greater than the forecasted decline. Unrated Securities Risk. Unrated securities determined by the Fund’s investment adviser to be of comparable quality to rated investments which the Fund may purchase may pay a higher dividend or interest rate than such rated investments and be subject to a greater risk of illiquidity or price changes. Less public information is typically available about unrated investments or issuers than rated investments or issuers. Some unrated securities may not have an active trading market or may be difficult to value, which means the Fund might have difficulty selling them promptly at an acceptable price. To the extent that the Fund invests in unrated securities, the Fund’s ability to achieve its investment objectives will be more dependent on the investment adviser’s credit analysis than would be the case when the Fund invests in rated securities. Valuation Risk. The municipal securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including readily available market quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to sell a portfolio security at the price established by the pricing service, which could result in a loss to the Fund. Pricing services generally price municipal securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Different pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s NAV. When-Issued and Delayed-Delivery Transactions Risk. When-issued and delayed-delivery transactions may involve an element of risk because no interest accrues on the securities prior to settlement and, because securities are subject to market fluctuations, the value of the securities at time of delivery may be less (or more) than their cost. A separate account of the Fund will be established with its custodian consisting of cash equivalents or liquid securities having a market value at all times at least equal to the amount of any delayed payment commitment. Zero Coupon Bonds Risk or Pay-In-Kind Securities Risk. Zero Coupon and pay-in-kind securities may be subject to greater fluctuation in value and less liquidity in the event of adverse market conditions than comparably rated securities paying cash interest at regular interest payment periods. Prices on non-cash-paying instruments may be more sensitive to changes in the issuer’s financial condition, fluctuation in interest rates and market demand/ supply imbalances than cash-paying securities with similar credit ratings, and thus may be more speculative. Fund Level and Other Risks: Anti-Takeover Provisions. The Declaration of Trust and the Fund’s by-laws include provisions that could limit the ability of other entities or persons to acquire control of the Fund or convert the Fund to open-end status. These provisions could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares. Counterparty Risk. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives or other transactions supported by another party’s credit will affect the value of those instruments. Certain entities that have served as counterparties in the markets for these transactions have incurred or may incur in the future significant financial hardships including bankruptcy and losses as a result of exposure to sub-prime mortgages and other lower-quality credit investments. As a result, such hardships have reduced these entities’ capital and called into question their continued ability to perform their obligations under such transactions. By using such derivatives or other transactions, the Fund assumes the risk that its counterparties could experience similar financial hardships. In the event of the insolvency of a counterparty, the Fund may sustain losses or be unable to liquidate a derivatives position. Cybersecurity Risk. The Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund. Economic and Political Events Risk. The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the municipal securities of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the creditworthiness and value of such municipal securities. Fund Tax Risk. The Fund has elected to be treated and intends to qualify each year as a Regulated Investment Company (“RIC”) under the Internal Revenue Code of 1986, as amended (the “Code”). As a RIC, the Fund is not expected to be subject to U.S. federal income tax to the extent that it distributes its investment company taxable income and net capital gains. To qualify for the special tax treatment available to a RIC, the Fund must comply with certain investment, distribution, and diversification requirements. Under certain circumstances, the Fund may be forced to sell certain assets when it is not advantageous in order to meet these requirements, which may reduce the Fund’s overall return. If the Fund fails to meet any of these requirements, subject to the opportunity to cure such failures under applicable provisions of the Code, the Fund’s income would be subject to a double level of U.S. federal income tax. The Fund’s income, including its net capital gain, would first be subject to U.S. federal income tax at regular corporate rates, even if such income were distributed to shareholders and, second, all distributions by the Fund from earnings and profits, including distributions of net capital gain (if any), would be taxable to shareholders as dividends. Global Economic Risk. National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and asset prices around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies, may have global negative economic and market repercussions. Additionally, instability in various countries, war, natural and environmental disasters, the spread of infectious illnesses or other public health emergencies, terrorist attacks in the United States and around the world, growing social and political discord in the United States, debt crises, the response of the international community—through economic sanctions and otherwise—to international events, further downgrade of U.S. government securities, changes in the U.S. president or political shifts in Congress, trade disputes and other similar events may adversely affect the global economy and the markets and issuers in which the Fund invests. These events could reduce consumer demand or economic output, result in market closure, travel restrictions or quarantines, and generally have a significant impact on the global economy. These events could also impair the information technology and other operational systems upon which the Fund’s service providers, including the Fund’s sub-adviser, rely, and could otherwise disrupt the ability of employees of the Fund’s service providers to perform essential tasks on behalf of the Fund. The Fund does not know and cannot predict how long the securities markets may be affected by these events, and the future impact of these and similar events on the global economy and securities markets is uncertain. The Fund may be adversely affected by abrogation of international agreements and national laws which have created the market instruments in which the Fund may invest, failure of the designated national and international authorities to enforce compliance with the same laws and agreements, failure of local, national and international organizations to carry out the duties prescribed to them under the relevant agreements, revisions of these laws and agreements which dilute their effectiveness or conflicting interpretation of provisions of the same laws and agreements. Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. Investment and Market Risk. An investment in common shares is subject to investment risk, including the possible loss of the entire principal amount that you invest. Common shares frequently trade at a discount to their NAV. An investment in common shares represents an indirect investment in the securities owned by the Fund. Common shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of Fund dividends and distributions. Legislation and Regulatory Risk. At any time after the date of this report, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, securities held by the Fund or the issuers of such securities. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objectives. Leverage Risk. The use of leverage creates special risks for common shareholders, including potential interest rate risks and the likelihood of greater volatility of NAV and market price of, and distributions on, the common shares. The use of leverage in a declining market will likely cause a greater decline in the Fund’s NAV, which may result at a greater decline of the common share price, than if the Fund were not to have used leverage. Certain types of leverage may result in the Fund being subject to certain covenants, asset coverage or other portfolio composition limits by its lenders, debt or preferred securities purchasers, rating agencies that may rate the debt or preferred securities, or reverse repurchase counterparties. Such limitations may be more stringent than those imposed by the 1940 Act and may impact whether the Fund is able to maintain its desired amount of leverage. In addition, whenever the Fund incurs borrowings and/or preferred shares are outstanding, Common Shareholders will not be entitled to receive any cash distributions from the Fund unless all interest on such borrowings has been paid and all accumulated dividends on preferred shares have been paid, unless asset coverage (as defined in the 1940 Act) with respect to any borrowings would be at least 300% after giving effect to the distributions and asset coverage (as defined in the 1940 Act) with respect to preferred shares would be at least 200% after giving effect to the distributions. The Fund will pay (and common shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the Fund’s NAV. The investment adviser may, based on its assessment of market conditions and composition of the Fund’s holdings, increase or decrease the amount of leverage. Such changes may impact the Fund’s distributions and the price of the common shares in the secondary market. There is no assurance that the Fund’s use of leverage will be successful. The Fund may seek to refinance its leverage over time, in the ordinary course, as current forms of leverage mature or it is otherwise desirable to refinance; however, the form that such leverage will take cannot be predicted at this time. If the Fund is unable to replace existing leverage on comparable terms, its costs of leverage will increase. Accordingly, there is no assurance that the use of leverage may result in a higher yield or return to common shareholders. The amount of fees paid to the investment adviser and the sub-adviser for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets – this may create an incentive for the investment adviser and the sub- adviser to leverage the Fund or increase the Fund’s leverage. Market Discount from Net Asset Value. Shares of closed-end investment companies like the Fund frequently trade at prices lower than their NAV. This characteristic is a risk separate and distinct from the risk that the Fund’s NAV could decrease as a result of investment activities. Whether investors will realize gains or losses upon the sale of the common shares will depend not upon the Fund’s NAV but entirely upon whether the market price of the common shares at the time of sale is above or below the investor’s purchase price for the common shares. Furthermore, management may have difficulty meeting the Fund’s investment objectives and managing its portfolio when the underlying securities are redeemed or sold during periods of market turmoil and as investors’ perceptions regarding closed-end funds or their underlying investments change. Because the market price of the common shares will be determined by factors such as relative supply of and demand for the common shares in the market, general market and economic circumstances, and other factors beyond the control of the Fund, the Fund cannot predict whether the common shares will trade at, below or above NAV. The common shares are designed primarily for long-term investors, and you should not view the Fund as a vehicle for short-term trading purposes. Recent Market Conditions. Periods of unusually high financial market volatility and restrictive credit conditions, at times limited to a particular sector or geographic area, have occurred in the past and may be expected to recur in the future. Some countries, including the United States, have adopted or have signaled protectionist trade measures, including the imposition of tariffs, relaxation of the financial industry regulations that followed the financial crisis, and/or reductions to corporate taxes. The scope of these policy changes is still developing, but the equity and debt markets may react strongly to expectations of change, which could increase volatility, particularly if a resulting policy runs counter to the market’s expectations. The outcome of such changes cannot be foreseen at the present time. In addition, geopolitical and other risks, including environmental and public health risks, may add to instability in the world economy and markets generally. As a result of increasingly interconnected global economies and financial markets, the value and liquidity of the Fund’s investments may be negatively affected by events impacting a country or region, regardless of whether the Fund invests in issuers located in or with significant exposure to such country or region. Ukraine has experienced ongoing military conflict, most recently commencing in February 2022 when Russia invaded Ukraine; this conflict may expand and military attacks could occur elsewhere in Europe. Europe has also been struggling with mass migration from the Middle East and Africa. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. Additionally, in October 2023 armed conflict broke out between Israel and the militant group Hamas after Hamas infiltrated Israel’s southern border from the Gaza Strip. Israel has since declared war against Hamas and this conflict has escalated into a greater regional conflict. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. The ongoing trade war between China and the United States, including the imposition of tariffs by each country on the other country’s products, has created a tense political environment. These actions may trigger a significant reduction in international trade, adverse effects in the supply of certain manufactured goods, substantial adverse price changes for goods and possible failure of individual companies and/or large segments of China’s export industry and U.S. importers, which could have a negative impact on the Fund’s performance. U.S. companies that source material and goods from China and those that make large amounts of sales in China are particularly vulnerable to an escalation of trade tensions. Beginning in early 2025, the United States also imposed tariffs on other countries, including Mexico and Canada. The possibility of additional tariffs being imposed or the outbreak of a trade war may adversely impact U.S. and international markets. Uncertainty regarding the outcome of the trade tensions and the potential for a trade war could cause the U.S. dollar to decline further. Events such as these and their consequences are difficult to predict and it is unclear whether further tariffs may be imposed or other escalating actions may be taken in the future. Additionally, political uncertainty regarding U.S. policy, including the U.S. government’s approach to trade, may impact the markets and the Fund’s performance. The U.S. Federal Reserve (the “Fed”) has in the past sharply raised interest rates, and has signaled an intention to maintain relatively higher interest rates until current inflation levels re-align with the Fed’s long-term inflation target. Changing interest rate environments impact the various sectors of the economy in different ways. For example, in March 2023, the Federal Deposit Insurance Corporation (“FDIC”) was appointed receiver for each of Silicon Valley Bank and Signature Bank, the second- and third-largest bank failures in U.S. history, which failures may be attributable, in part, to rising interest rates. Bank failures may have a destabilizing impact on the broader banking industry or markets generally. The impact of these developments in the near- and long-term is unknown and could have additional adverse effects on economies, financial markets and asset valuations around the world. Reverse Repurchase Agreement Risk. A reverse repurchase agreement, in economic essence, constitutes a securitized borrowing by the Fund from the security purchaser. The Fund may enter into reverse repurchase agreements for the purpose of creating a leveraged investment exposure and, as such, their usage involves essentially the same risks associated with a leveraging strategy generally since the proceeds from these agreements may be invested in additional portfolio securities. Reverse repurchase agreements tend to be short-term in tenor, and there can be no assurances that the purchaser (lender) will commit to extend or “roll” a given agreement upon its agreed-upon repurchase date or an alternative purchaser can be identified on similar terms. Reverse repurchase agreements also involve the risk that the purchaser fails to return the securities as agreed upon, files for bankruptcy or becomes insolvent. The Fund may be restricted from taking normal portfolio actions during such time, could be subject to loss to the extent that the proceeds of the agreement are less than the value of securities subject to the agreement and may experience adverse tax consequences. |  |  |  |  |  |  |  |
Effects of Leverage [Text Block] |  |  |  |  |  |  |  |  |  |  | EFFECTS OF LEVERAGE The following table is furnished in response to requirements of the SEC. It is designed to illustrate the effects of leverage through the use of senior securities, as that term is defined under Section 18 of the 1940 Act, as well as certain other forms of leverage, such as reverse repurchase agreements and investments in inverse floating rate securities, on common share total return, assuming investment portfolio total returns (consisting of income and changes in the value of investments held in a Fund’s portfolio) of -10%, -5%, 0%, 5% and 10%. The table below reflects each Fund’s (i) continued use of leverage as of August 31, 2025 as a percentage of Managed Assets (including assets attributable to such leverage), (ii) the estimated annual effective interest expense rate payable by the Fund on such instruments (based on actual leverage costs incurred during the fiscal year ended August 31, 2025) as set forth in the table, and (iii) the annual return that the Fund’s portfolio must experience (net of expenses) in order to cover such costs of leverage based on such estimated annual effective interest expense rate. The information below does not reflect any Fund’s use of certain other forms of economic leverage achieved through the use of other instruments or transactions not considered to be senior securities under the 1940 Act, such as certain derivative instruments and investments in inverse floating rate securities. The numbers are merely estimates, used for illustration. The costs of leverage may vary frequently and may be significantly higher or lower than the estimated rate. The assumed investment portfolio returns in the table below are hypothetical figures and are not necessarily indicative of the investment portfolio returns experienced or expected to be experienced by the Fund. Your actual returns may be greater or less than those appearing below.
|  |  | NAZ |  |  |  | NKX |  |  |  | NAC |  |  |  | NXJ |  |  |  | NRK |  |  |  | NAN |  |  |  | NQP |
Estimated Leverage as a Percentage of Managed Assets (Including Assets Attributable to Leverage) |  |  | 39.62 | % |  |  | 42.86 | % |  |  | 42.88 | % |  |  | 42.78 | % |  |  | 42.97 | % |  |  | 42.04 | % |  |  | 42.46 | %
Estimated Annual Effective Leverage Expense Rate Payable by Fund on Leverage |  |  | 3.75 | % |  |  | 3.69 | % |  |  | 3.89 | % |  |  | 3.86 | % |  |  | 3.75 | % |  |  | 3.91 | % |  |  | 3.78 | %
Annual Return Fund Portfolio Must Experience (net of expenses) to Cover Estimated Annual Effective Interest Expense Rate on Leverage |  |  | 1.48 | % |  |  | 1.58 | % |  |  | 1.67 | % |  |  | 1.65 | % |  |  | 1.61 | % |  |  | 1.65 | % |  |  | 1.61 | %
Common Share Total Return for (10.00)% Assumed Portfolio Total Return |  |  | (19.02 | )% |  |  | (20.27 | )% |  |  | (20.42 | )% |  |  | (20.36 | )% |  |  | (20.36 | )% |  |  | (20.09 | )% |  |  | (20.17 | )%
Common Share Total Return for (5.00)% Assumed Portfolio Total Return |  |  | (10.74 | )% |  |  | (11.52 | )% |  |  | (11.67 | )% |  |  | (11.62 | )% |  |  | (11.59 | )% |  |  | (11.47 | )% |  |  | (11.48 | )%
Common Share Total Return for 0.00% Assumed Portfolio Total Return |  |  | (2.46 | )% |  |  | (2.77 | )% |  |  | (2.92 | )% |  |  | (2.89 | )% |  |  | (2.83 | )% |  |  | (2.84 | )% |  |  | (2.79 | )%
Common Share Total Return for 5.00% Assumed Portfolio Total Return |  |  | 5.82 | % |  |  | 5.98 | % |  |  | 5.84 | % |  |  | 5.85 | % |  |  | 5.94 | % |  |  | 5.79 | % |  |  | 5.90 | %
Common Share Total Return for 10.00% Assumed Portfolio Total Return |  |  | 14.10 | % |  |  | 14.73 | % |  |  | 14.59 | % |  |  | 14.59 | % |  |  | 14.71 | % |  |  | 14.41 | % |  |  | 14.59 | %
Common Share total return is composed of two elements — the distributions paid by a Fund to holders of common shares (the amount of which is largely determined by the net investment income of the Fund after paying dividend payments on any preferred shares issued by the Fund and expenses on any forms of leverage outstanding) and gains or losses on the value of the securities and other instruments the Fund owns. As required by SEC rules, the table assumes that a Fund is more likely to suffer capital losses than to enjoy capital appreciation. For example, to assume a total return of 0%, a Fund must assume that the income it receives on its investments is entirely offset by losses in the value of those investments. This table reflects hypothetical performance of a Fund’s portfolio and not the actual performance of the Fund’s common shares, the value of which is determined by market forces and other factors. Should a Fund elect to add additional leverage to its portfolio, any benefits of such additional leverage cannot be fully achieved until the proceeds resulting from the use of such leverage have been received by the Fund and invested in accordance with the Fund’s investment objectives and policies. As noted above, a Fund’s willingness to use additional leverage, and the extent to which leverage is used at any time, will depend on many factors. |  |  |  |  |  |  |  |
Annual Interest Rate [Percent] |  |  |  |  |  |  |  |  |  |  | 39.62% |  |  |  |  |  |  |  |
Annual Interest Rate, Current [Percent] |  |  |  |  |  |  |  |  |  |  | 3.75% |  |  |  |  |  |  |  |
Annual Coverage Return Rate [Percent] |  |  |  |  |  |  |  |  |  |  | 1.48% |  |  |  |  |  |  |  |
Effects of Leverage [Table Text Block] |  |  |  |  |  |  |  |  |  |  | The numbers are merely estimates, used for illustration. The costs of leverage may vary frequently and may be significantly higher or lower than the estimated rate. The assumed investment portfolio returns in the table below are hypothetical figures and are not necessarily indicative of the investment portfolio returns experienced or expected to be experienced by the Fund. Your actual returns may be greater or less than those appearing below.
|  |  | NAZ |  |  |  | NKX |  |  |  | NAC |  |  |  | NXJ |  |  |  | NRK |  |  |  | NAN |  |  |  | NQP |
Estimated Leverage as a Percentage of Managed Assets (Including Assets Attributable to Leverage) |  |  | 39.62 | % |  |  | 42.86 | % |  |  | 42.88 | % |  |  | 42.78 | % |  |  | 42.97 | % |  |  | 42.04 | % |  |  | 42.46 | %
Estimated Annual Effective Leverage Expense Rate Payable by Fund on Leverage |  |  | 3.75 | % |  |  | 3.69 | % |  |  | 3.89 | % |  |  | 3.86 | % |  |  | 3.75 | % |  |  | 3.91 | % |  |  | 3.78 | %
Annual Return Fund Portfolio Must Experience (net of expenses) to Cover Estimated Annual Effective Interest Expense Rate on Leverage |  |  | 1.48 | % |  |  | 1.58 | % |  |  | 1.67 | % |  |  | 1.65 | % |  |  | 1.61 | % |  |  | 1.65 | % |  |  | 1.61 | %
Common Share Total Return for (10.00)% Assumed Portfolio Total Return |  |  | (19.02 | )% |  |  | (20.27 | )% |  |  | (20.42 | )% |  |  | (20.36 | )% |  |  | (20.36 | )% |  |  | (20.09 | )% |  |  | (20.17 | )%
Common Share Total Return for (5.00)% Assumed Portfolio Total Return |  |  | (10.74 | )% |  |  | (11.52 | )% |  |  | (11.67 | )% |  |  | (11.62 | )% |  |  | (11.59 | )% |  |  | (11.47 | )% |  |  | (11.48 | )%
Common Share Total Return for 0.00% Assumed Portfolio Total Return |  |  | (2.46 | )% |  |  | (2.77 | )% |  |  | (2.92 | )% |  |  | (2.89 | )% |  |  | (2.83 | )% |  |  | (2.84 | )% |  |  | (2.79 | )%
Common Share Total Return for 5.00% Assumed Portfolio Total Return |  |  | 5.82 | % |  |  | 5.98 | % |  |  | 5.84 | % |  |  | 5.85 | % |  |  | 5.94 | % |  |  | 5.79 | % |  |  | 5.90 | %
Common Share Total Return for 10.00% Assumed Portfolio Total Return |  |  | 14.10 | % |  |  | 14.73 | % |  |  | 14.59 | % |  |  | 14.59 | % |  |  | 14.71 | % |  |  | 14.41 | % |  |  | 14.59 | %
Return at Minus Ten [Percent] |  |  |  |  |  |  |  |  |  |  | (19.02%) |  |  |  |  |  |  |  |
Return at Minus Five [Percent] |  |  |  |  |  |  |  |  |  |  | (10.74%) |  |  |  |  |  |  |  |
Return at Zero [Percent] |  |  |  |  |  |  |  |  |  |  | (2.46%) |  |  |  |  |  |  |  |
Return at Plus Five [Percent] |  |  |  |  |  |  |  |  |  |  | 5.82% |  |  |  |  |  |  |  |
Return at Plus Ten [Percent] |  |  |  |  |  |  |  |  |  |  | 14.10% |  |  |  |  |  |  |  |
Effects of Leverage, Purpose [Text Block] |  |  |  |  |  |  |  |  |  |  | The following table is furnished in response to requirements of the SEC. It is designed to illustrate the effects of leverage through the use of senior securities, as that term is defined under Section 18 of the 1940 Act, as well as certain other forms of leverage, such as reverse repurchase agreements and investments in inverse floating rate securities, on common share total return, assuming investment portfolio total returns (consisting of income and changes in the value of investments held in a Fund’s portfolio) of -10%, -5%, 0%, 5% and 10%. The table below reflects each Fund’s (i) continued use of leverage as of August 31, 2025 as a percentage of Managed Assets (including assets attributable to such leverage), (ii) the estimated annual effective interest expense rate payable by the Fund on such instruments (based on actual leverage costs incurred during the fiscal year ended August 31, 2025) as set forth in the table, and (iii) the annual return that the Fund’s portfolio must experience (net of expenses) in order to cover such costs of leverage based on such estimated annual effective interest expense rate. The information below does not reflect any Fund’s use of certain other forms of economic leverage achieved through the use of other instruments or transactions not considered to be senior securities under the 1940 Act, such as certain derivative instruments and investments in inverse floating rate securities. |  |  |  |  |  |  |  |
Share Price [Table Text Block] |  |  |  |  |  |  |  |  |  |  | The following table shows for the periods indicated: (i) the high and low sales prices for the Common Shares reported as of the end of the day on the NYSE, (ii) the corresponding NAV per share; and (iii) the premium/(discount) to NAV per share at which the Common Shares were trading as of such date. NAZ
|  | Closing Market Price per Common Share |  |  | NAV per Common Share on Date of Market Price |  |  | Premium/(Discount) on Date of Market Price |
Fiscal Quarter Ended |  | High |  |  | Low |  |  | High |  |  | Low |  |  | High |  |  | Low |
August 2025 |  |  | $11.90 |  |  |  | $11.51 |  |  |  | $11.07 |  |  |  | $11.22 |  |  |  | 7.50% |  |  |  | 2.58% |
May 2025 |  |  | $13.44 |  |  |  | $11.45 |  |  |  | $12.16 |  |  |  | $11.20 |  |  |  | 10.53% |  |  |  | 2.23% |
February 2025 |  |  | $12.70 |  |  |  | $11.28 |  |  |  | $12.17 |  |  |  | $12.09 |  |  |  | 4.35% |  |  |  | (6.70)% |
November 2024 |  |  | $12.29 |  |  |  | $11.54 |  |  |  | $12.49 |  |  |  | $12.35 |  |  |  | (1.60)% |  |  |  | (6.56)% |
August 2024 |  |  | $11.77 |  |  |  | $10.68 |  |  |  | $12.73 |  |  |  | $12.33 |  |  |  | (7.54)% |  |  |  | (13.38)% |
May 2024 |  |  | $11.05 |  |  |  | $10.55 |  |  |  | $12.76 |  |  |  | $12.33 |  |  |  | (13.40)% |  |  |  | (14.44)% |
February 2024 |  |  | $10.94 |  |  |  | $10.57 |  |  |  | $12.63 |  |  |  | $12.39 |  |  |  | (13.38)% |  |  |  | (14.69)% |
November 2023 |  |  | $10.47 |  |  |  | $9.26 |  |  |  | $12.36 |  |  |  | $11.20 |  |  |  | (15.29)% |  |  |  | (17.32)% |
NKX
|  | Closing Market Price per Common Share |  |  | NAV per Common Share on Date of Market Price |  |  | Premium/(Discount) on Date of Market Price |
Fiscal Quarter Ended |  | High |  |  | Low |  |  | High |  |  | Low |  |  | High |  |  | Low |
August 2025 |  |  | $12.07 |  |  |  | $11.46 |  |  |  | $11.61 |  |  |  | $11.74 |  |  |  | 3.96% |  |  |  | (2.39)% |
May 2025 |  |  | $13.05 |  |  |  | $11.70 |  |  |  | $12.83 |  |  |  | $11.65 |  |  |  | 1.71% |  |  |  | 0.43% |
February 2025 |  |  | $13.08 |  |  |  | $12.30 |  |  |  | $13.24 |  |  |  | $12.83 |  |  |  | (1.21)% |  |  |  | (4.13)% |
November 2024 |  |  | $14.06 |  |  |  | $12.85 |  |  |  | $13.37 |  |  |  | $13.17 |  |  |  | 5.16% |  |  |  | (2.43)% |
August 2024 |  |  | $13.40 |  |  |  | $11.48 |  |  |  | $13.26 |  |  |  | $12.90 |  |  |  | 1.06% |  |  |  | (11.01)% |
May 2024 |  |  | $12.23 |  |  |  | $11.40 |  |  |  | $13.26 |  |  |  | $12.89 |  |  |  | (7.77)% |  |  |  | (11.56)% |
February 2024 |  |  | $11.65 |  |  |  | $11.24 |  |  |  | $13.45 |  |  |  | $13.12 |  |  |  | (13.38)% |  |  |  | (14.33)% |
November 2023 |  |  | $11.57 |  |  |  | $9.80 |  |  |  | $12.50 |  |  |  | $11.69 |  |  |  | (7.44)% |  |  |  | (16.17)% |
NAC
|  | Closing Market Price per Common Share |  |  | NAV per Common Share on Date of Market Price |  |  | Premium/(Discount) on Date of Market Price |
Fiscal Quarter Ended |  | High |  |  | Low |  |  | High |  |  | Low |  |  | High |  |  | Low |
August 2025 |  |  | $11.33 |  |  |  | $10.88 |  |  |  | $11.10 |  |  |  | $11.22 |  |  |  | 2.07% |  |  |  | (3.03)% |
May 2025 |  |  | $11.61 |  |  |  | $10.51 |  |  |  | $12.34 |  |  |  | $11.18 |  |  |  | (5.92)% |  |  |  | (5.99)% |
February 2025 |  |  | $11.88 |  |  |  | $11.12 |  |  |  | $12.79 |  |  |  | $12.27 |  |  |  | (7.11)% |  |  |  | (9.37)% |
November 2024 |  |  | $11.99 |  |  |  | $11.34 |  |  |  | $12.93 |  |  |  | $12.57 |  |  |  | (7.27)% |  |  |  | (9.79)% |
August 2024 |  |  | $11.81 |  |  |  | $10.94 |  |  |  | $12.87 |  |  |  | $12.44 |  |  |  | (8.24)% |  |  |  | (12.06)% |
May 2024 |  |  | $11.17 |  |  |  | $10.64 |  |  |  | $12.92 |  |  |  | $12.57 |  |  |  | (13.54)% |  |  |  | (15.35)% |
February 2024 |  |  | $11.15 |  |  |  | $10.67 |  |  |  | $12.92 |  |  |  | $12.60 |  |  |  | (13.70)% |  |  |  | (15.32)% |
November 2023 |  |  | $10.65 |  |  |  | $9.33 |  |  |  | $12.40 |  |  |  | $11.21 |  |  |  | (14.11)% |  |  |  | (16.77)% |
NAN
|  | Closing Market Price per Common Share |  |  | NAV per Common Share on Date of Market Price |  |  | Premium/(Discount) on Date of Market Price |
Fiscal Quarter Ended |  | High |  |  | Low |  |  | High |  |  | Low |  |  | High |  |  | Low |
August 2025 |  |  | $11.47 |  |  |  | $10.83 |  |  |  | $11.13 |  |  |  | $10.77 |  |  |  | 3.05% |  |  |  | 0.56% |
May 2025 |  |  | $11.85 |  |  |  | $10.86 |  |  |  | $12.09 |  |  |  | $11.11 |  |  |  | (1.99)% |  |  |  | (2.25)% |
February 2025 |  |  | $11.82 |  |  |  | $11.09 |  |  |  | $12.10 |  |  |  | $12.05 |  |  |  | (2.31)% |  |  |  | (7.97)% |
November 2024 |  |  | $11.89 |  |  |  | $11.28 |  |  |  | $12.67 |  |  |  | $12.27 |  |  |  | (6.16)% |  |  |  | (8.07)% |
August 2024 |  |  | $11.54 |  |  |  | $10.65 |  |  |  | $12.50 |  |  |  | $12.20 |  |  |  | (7.68)% |  |  |  | (12.70)% |
May 2024 |  |  | $11.03 |  |  |  | $10.57 |  |  |  | $12.72 |  |  |  | $12.18 |  |  |  | (13.29)% |  |  |  | (13.22)% |
February 2024 |  |  | $11.17 |  |  |  | $10.50 |  |  |  | $12.76 |  |  |  | $12.35 |  |  |  | (12.46)% |  |  |  | (14.98)% |
November 2023 |  |  | $10.49 |  |  |  | $9.14 |  |  |  | $12.24 |  |  |  | $11.01 |  |  |  | (14.30)% |  |  |  | (16.98)% |
The following table shows, as of August 31, 2025 each Fund’s: (i) NAV per Common Share, (ii) market price, (iii) percentage of premium/(discount) to NAV per Common Share and, (iv) net assets attributable to Common Shares.
August 31, 2025 |  | NAZ |  |  | NKX |  |  | NAC |  |  | NAN |
NAV per Common Share |  |  | $ 11.12 |  |  |  | $ 11.56 |  |  |  | $ 11.06 |  |  |  | $ 10.88 |
Market Price |  |  | $ 11.86 |  |  |  | $ 11.82 |  |  |  | $ 11.23 |  |  |  | $ 10.97 |
Percentage of Premium/(Discount) to NAV per Common Share |  |  | 6.65% |  |  |  | 2.25% |  |  |  | 1.54% |  |  |  | 0.83% |
Net Assets Attributable to Common Shares |  |  | $ 134,580,896 |  |  |  | $ 574,400,459 |  |  |  | $ 1,611,347,880 |  |  |  | $ 337,745,923 |
Shares of closed-end investment companies, including those of the Funds, may frequently trade at prices lower than NAV, the Funds’ Board of Trustees (Board) has currently determined that, at least annually, it will consider action that might be taken to reduce or eliminate any material discount from NAV in respect of Common Shares, which may include the repurchase of such shares in the open market or in private transactions, the making of a tender offer for such shares at NAV, or the conversion of the Fund to an open-end investment company. The Funds cannot assure you that their Board will decide to take any of these actions, or that share repurchases or tender offers will actually reduce market discount. |  |  |  |  |  |  |  |
Latest Premium (Discount) to NAV [Percent] |  |  |  |  |  |  |  |  |  |  | 6.65% |  |  |  |  |  |  |  |
Alternative Minimum Tax Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Alternative Minimum Tax Risk. As a result of the Fund’s investments in AMT Bonds, a portion of the Fund’s otherwise exempt-interest dividends may be taxable to those shareholders subject to the federal alternative minimum tax. |  |  |  |  |  |  |  |
Below Investment Grade Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Below Investment Grade Risk. Municipal securities of below investment grade quality are regarded as having speculative characteristics with respect to the issuer’s capacity to pay dividends or interest and repay principal, and may be subject to higher price volatility and default risk than investment grade municipal securities of comparable terms and duration. Issuers of lower grade municipal securities may be highly leveraged and may not have available to them more traditional methods of financing. The prices of these lower grade securities are typically more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn. The secondary market for lower rated municipal securities may not be as liquid as the secondary market for more highly rated municipal securities, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular municipal security. If a below investment grade municipal security goes into default, or its issuer enters bankruptcy, it might be difficult to sell that security in a timely manner at a reasonable price. |  |  |  |  |  |  |  |
Call Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Call Risk. The Fund may invest in municipal securities that are subject to call risk. Such municipal securities may be redeemed at the option of the issuer, or “called,” before their stated maturity or redemption date. In general, an issuer will call its instruments if they can be refinanced by issuing new instruments that bear a lower interest rate. The Fund is subject to the possibility that during periods of falling interest rates, an issuer will call its high yielding municipal securities. The Fund would then be forced to invest the unanticipated proceeds at lower interest rates, resulting in a decline in the Fund’s income. |  |  |  |  |  |  |  |
Credit Risks [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Credit Risk. Issuers of municipal securities in which the Fund may invest may default on their obligations, including to pay principal or interest when due. This non-payment would result in a reduction of income to the Fund, a reduction in the value of a municipal security experiencing non-payment and potentially a decrease in the net asset value (“NAV”) of the Fund. To the extent that the credit rating assigned to a municipal security in the Fund’s portfolio is downgraded, the market price and liquidity of such security may be adversely affected. |  |  |  |  |  |  |  |
Credit Spread Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Credit Spread Risk. Credit spread risk is the risk that credit spreads (i.e., the difference in yield between securities that is due to differences in their credit quality) may increase when the market believes that municipal securities generally have a greater risk of default. Increasing credit spreads may reduce the market values of the Fund’s securities. Credit spreads often increase more for lower rated and unrated securities than for investment grade securities. In addition, when credit spreads increase, reductions in market value will generally be greater for longer-maturity securities. |  |  |  |  |  |  |  |
Deflation Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Deflation Risk. Deflation risk is the risk that prices throughout the economy decline over time. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. |  |  |  |  |  |  |  |
Derivatives Risks [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Derivatives Risk. The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a municipal security or other asset without buying or selling the municipal security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over-the-counter derivative transaction between the Fund and a counterparty that is not cleared through a central counterparty also involves the risk that a loss may be sustained as a result of the failure of the counterparty to the contract to make required payments. The payment obligation for a cleared derivative transaction is guaranteed by a central counterparty, which exposes the Fund to the creditworthiness of the central counterparty. The use of certain derivatives involves leverage, which can cause the Fund’s portfolio to be more volatile than if the portfolio had not been leveraged. Leverage can significantly magnify the effect of price movements of the reference asset, disproportionately increasing the Fund’s losses and reducing the Fund’s opportunities for gains when the reference asset changes in unexpected ways. In some instances, such leverage could result in losses that exceed the original amount invested. It is possible that regulatory or other developments in the derivatives market, including changes in government regulation, could adversely impact the Fund’s ability to invest in certain derivatives or successfully use derivative instruments. |  |  |  |  |  |  |  |
Distressed or Defaulted Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Distressed or Defaulted Securities Risk. Investments in “distressed” securities, meaning those whose issuers are experiencing financial difficulties or distress at the time the security is acquired, present a substantial risk of future default. In the event distressed securities become defaulted securities or the Fund otherwise holds defaulted securities, the Fund may incur losses, including additional expenses, to the extent it is required to seek recovery upon a default in the payment of principal or interest on those investments. In any reorganization or liquidation proceeding relating to a portfolio investment, the Fund may lose its entire investment or may be required to accept cash or securities with a value less than its original investment. Defaulted or distressed securities may be subject to restrictions on resale. |  |  |  |  |  |  |  |
Duration Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Duration Risk. Duration is the sensitivity, expressed in years, of the price of a fixed-income security to changes in the general level of interest rates (or yields). Securities with longer durations tend to be more sensitive to interest rate (or yield) changes, which typically corresponds to increased volatility and risk, than securities with shorter durations. For example, if a security or portfolio has a duration of three years and interest rates increase by 1%, then the security or portfolio would decline in value by approximately 3%. Duration differs from maturity in that it considers potential changes to interest rates, and a security’s coupon payments, yield, price and par value and call features, in addition to the amount of time until the security matures. The duration of a security will be expected to change over time with changes in market factors and time to maturity. |  |  |  |  |  |  |  |
Economic Sector Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Economic Sector Risk. The Fund may invest a significant amount of its total assets in municipal securities in the same economic sector. This may make the Fund more susceptible to adverse economic, political or regulatory occurrences affecting an economic sector, making the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. As the percentage of the Fund’s Managed Assets invested in a particular sector increases, so does the potential for fluctuation in the value of the Fund’s assets. In addition, the Fund may invest a significant portion of its assets in certain sectors of the municipal securities market, such as health care facilities, private educational facilities, special taxing districts and start-up utility districts, and private activity bonds including industrial development bonds on behalf of transportation companies, whose credit quality and performance may be more susceptible to economic, business, political, regulatory and other developments than other sectors of municipal issuers. If the Fund invests a significant portion of its assets in one or more particular sectors, the Fund’s performance may be subject to additional risk and variability. |  |  |  |  |  |  |  |
Floating and Variable Rate Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Floating and Variable Rate Securities Risk. Floating and variable rate securities provide for adjustment in the interest rate paid on the obligations. The terms of such obligations typically provide that interest rates are adjusted based upon an interest or market rate adjustment as provided in the respective obligations. The adjustment intervals may be regular, and range from daily up to annually, or may be event-based, such as based on a change in the prime rate. Because of the interest rate adjustment feature, floating and variable rate securities provide an investor with a certain degree of protection against rises in interest rates, although the investor will participate in any declines in interest rates as well. Generally, changes in interest rates will have a smaller effect on the market value of floating and variable rate securities than on the market value of comparable fixed-income obligations. Thus, investing in floating and variable rate securities generally allows less opportunity for capital appreciation and depreciation than investing in comparable fixed-income securities. Floating and variable rate securities may be subject to greater liquidity risk than other debt securities, meaning that there may be limitations on the Fund’s ability to sell the securities at any given time. Such securities also may lose value. |  |  |  |  |  |  |  |
Financial Futures and Options Transactions Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Financial Futures and Options Transactions Risk. The Fund may use certain transactions for hedging the portfolio’s exposure to credit risk and the risk of increases in interest rates, which could result in poorer overall performance for the Fund. There may be an imperfect correlation between price movements of the futures and options and price movements of the portfolio securities being hedged. If the Fund engages in futures transactions or in the writing of options on futures, it will be required to maintain initial margin and maintenance margin and may be required to make daily variation margin payments in accordance with applicable rules of the exchanges and the Commodity Futures Trading Commission (“CFTC”). If the Fund purchases a financial futures contract or a call option or writes a put option in order to hedge the anticipated purchase of municipal securities, and if the Fund fails to complete the anticipated purchase transaction, the Fund may have a loss or a gain on the futures or options transaction that will not be offset by price movements in the municipal securities that were the subject of the anticipatory hedge. There can be no assurance that a liquid market will exist at a time when the Fund seeks to close out a derivatives or futures or a futures option position, and the Fund would remain obligated to meet margin requirements until the position is closed. |  |  |  |  |  |  |  |
Hedging Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Hedging Risk. The Fund’s use of derivatives or other transactions to reduce risk involves costs and will be subject to the investment adviser’s and/or the sub-adviser’s ability to predict correctly changes in the relationships of such hedge instruments to the Fund’s portfolio holdings or other factors. No assurance can be given that the investment adviser’s and/or the sub-adviser’s judgment in this respect will be correct, and no assurance can be given that the Fund will enter into hedging or other transactions at times or under circumstances in which it may be advisable to do so. Hedging activities may reduce the Fund’s opportunities for gain by offsetting the positive effects of favorable price movements and may result in net losses. |  |  |  |  |  |  |  |
Income Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Income Risk. The Fund’s level of current income could decline due to falling market interest rates. This is because, in a falling interest rate environment, the Fund generally will have to invest the proceeds from maturing portfolio securities in lower-yielding securities. |  |  |  |  |  |  |  |
Inflation Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Inflation Risk. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the common shares and distributions can decline. Currently, inflation rates are elevated relative to normal market conditions and could increase. |  |  |  |  |  |  |  |
Insurance Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Insurance Risk. The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub-prime mortgages and other lower credit quality investments. As a result, such losses reduced the insurers’ capital and called into question their continued ability to perform their obligations under such insurance if they are called upon to do so in the future. While an insured municipal security will typically be deemed to have the rating of its insurer, if the insurer of a municipal security suffers a downgrade in its credit rating or the market discounts the value of the insurance provided by the insurer, the value of the municipal security would more closely, if not entirely, reflect such rating. In such a case, the value of insurance associated with a municipal security may not add any value. The insurance feature of a municipal security does not guarantee the full payment of principal and interest through the life of an insured obligation, the market value of the insured obligation or the NAV of the common shares represented by such insured obligation. |  |  |  |  |  |  |  |
Interest Rate Risks [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Interest Rate Risk. Interest rate risk is the risk that municipal securities in the Fund’s portfolio will decline in value because of changes in market interest rates. Generally, when market interest rates rise, the market value of such securities will fall, and vice versa. As interest rates decline, issuers of municipal securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower-yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower than expected principal payments may extend the average life of municipal securities, potentially locking in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer- term municipal securities generally fluctuate more than prices of shorter-term municipal securities as interest rates change. If the Fund invests in floating rate securities, the market value of such securities may fall in a declining interest rate environment and may also fall in a rising interest rate environment if there is a lag between the rise in interest rates and the reset. A secondary risk associated with declining interest rates is the risk that income earned by the Fund on floating rate securities may decline due to lower coupon payments on floating-rate securities. |  |  |  |  |  |  |  |
Inverse Floating Rate Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Inverse Floating Rate Securities Risk. In general, income on inverse floating rate securities will decrease when short-term interest rates increase and increase when short-term interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal. In addition, inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of fixed rate securities. The Fund may invest in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities. The Fund may be required to sell its inverse floating rate securities at less than favorable prices, or liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following:
| • |  | If the Fund has a need for cash and the securities in a special purpose trust are not actively trading due to adverse market conditions;
| • |  | If special purpose trust sponsors (as a collective group or individually) experience financial hardship and consequently seek to terminate their respective outstanding special purpose trusts; and
| • |  | If the value of an underlying security declines significantly and if additional collateral has not been posted by the Fund.
Municipal Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Municipal Securities Risk. The values of municipal securities may be adversely affected by local political and economic conditions and developments. Adverse conditions in an industry significant to a local economy could have a correspondingly adverse effect on the financial condition of local issuers. Other factors that could affect municipal securities include a change in the local, state, or national economy, a downgrade of a state’s credit rating or the rating of authorities or political subdivisions of the state, demographic factors, ecological or environmental concerns, inability or perceived inability of a government authority to collect sufficient tax or other revenues, statutory limitations on the issuer’s ability to increase taxes, and other developments generally affecting the revenue of issuers (for example, legislation or court decisions reducing state aid to local governments or mandating additional services). This risk would be heightened to the extent that the Fund invests a substantial portion of the below-investment grade quality portion of its portfolio in the bonds of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), in industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, municipal lease obligations, private activity bonds or moral obligation bonds) that are particularly exposed to specific types of adverse economic, business or political events. The value of municipal securities may also be adversely affected by rising health care costs, increasing unfunded pension liabilities, and by the phasing out of federal programs providing financial support. In recent periods, a number of municipal issuers have defaulted on obligations, been downgraded or commenced insolvency proceedings. Financial difficulties of municipal issuers may continue or get worse. In addition, the amount of public information available about municipal bonds is generally less than for certain corporate equities or bonds, meaning that the investment performance of the Fund may be more dependent on the analytical abilities of the Fund’s sub‑adviser than funds that invest in stock or other corporate investments. To the extent that a fund invests a significant portion of its assets in the securities of issuers located in a given state or U.S. territory, it will be disproportionally affected by political and economic conditions and developments in that state or territory and may involve greater risk than funds that invest in a larger universe of securities. In addition, economic, political or regulatory changes in that state or territory could adversely affect municipal securities issuers in that state or territory and therefore the value of a fund’s investment portfolio. |  |  |  |  |  |  |  |
Municipal Securities Market Liquidity Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Municipal Securities Market Liquidity Risk. Inventories of municipal securities held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell municipal securities at attractive prices, and increase municipal security price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of municipal securities to raise cash to meet its obligations, those sales could further reduce the municipal securities’ prices and hurt performance. |  |  |  |  |  |  |  |
Municipal Securities Market Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Municipal Securities Market Risk. The amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the investment performance of the Fund may therefore be more dependent on the analytical abilities of the sub-adviser than if the Fund were a stock fund or taxable bond fund. The secondary market for municipal securities, particularly below investment grade municipal securities, also tends to be less well-developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell its municipal securities at attractive prices. |  |  |  |  |  |  |  |
Other Investment Companies Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Other Investment Companies Risk. Investing in an investment company exposes the Fund to all of the risks of that investment company’s investments. The Fund, as a holder of the securities of other investment companies, will bear its pro rata portion of the other investment companies’ expenses, including advisory fees. These expenses are in addition to the direct expenses of the Fund’s own operations. As a result, the cost of investing in investment company shares may exceed the costs of investing directly in its underlying investments. In addition, securities of other investment companies may be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities and therefore magnify the Fund’s leverage risk. With respect to ETF’s, an ETF that is based on a specific index may not be able to replicate and maintain exactly the composition and relative weighting of securities in the index. The value of an ETF based on a specific index is subject to change as the values of its respective component assets fluctuate according to market volatility. ETFs typically rely on a limited pool of authorized participants to create and redeem shares, and an active trading market for ETF shares may not develop or be maintained. The market value of shares of ETFs and closed-end funds may differ from their NAV. |  |  |  |  |  |  |  |
Puerto Rico Municipal Securities Market Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Puerto Rico Municipal Securities Market Risk. To the extent that the Fund invests a significant portion of its assets in the securities issued by the Commonwealth of Puerto Rico or its political subdivisions, agencies, instrumentalities, or public corporations (collectively referred to as “Puerto Rico” or the “Commonwealth”), it will be disproportionally affected by political, social and economic conditions and developments in the Commonwealth. In addition, economic, political or regulatory changes in that territory could adversely affect the value of the Fund’s investment portfolio. Puerto Rico currently is experiencing significant fiscal and economic challenges, including substantial debt service obligations, high levels of unemployment, underfunded public retirement systems, and persistent government budget deficits. These challenges may negatively affect the value of the Fund’s investments in Puerto Rican municipal securities. Several major ratings agencies have downgraded the general obligation debt of Puerto Rico to below investment grade and continue to maintain a negative outlook for this debt, which increases the likelihood that the rating will be lowered further. In both August 2015 and January 2016, Puerto Rico defaulted on its debt by failing to make full payment due on its outstanding bonds, and there can be no assurance that Puerto Rico will be able to satisfy its future debt obligations. Further downgrades or defaults may place additional strain on the Puerto Rico economy and may negatively affect the value, liquidity, and volatility of the Fund’s investments in Puerto Rican municipal securities. Additionally, numerous issuers have entered Title III of the Puerto Rico Oversite, Management and Economic Stability Act (“PROMESA”), which is similar to bankruptcy protection, through which the Commonwealth of Puerto Rico can restructure its debt. While most of Puerto Rico’s debt has been restructured, proceedings under PROMESA remain ongoing, and it is unclear at this time how those proceedings will be resolved or what impact they will have on the value of the Fund’s investments in Puerto Rico municipal securities. There can be no assurances that these debt restructuring efforts will be effective or that Puerto Rico will be able to service debt payments following the completion of such debt restructuring. In addition, any restructurings approved by a federal court could be appealed and overturned. The mediation process and certain litigation is ongoing with respect to certain municipal securities issued by Puerto Rico and its political subdivisions, instrumentalities and authorities. It is not presently possible to predict the results of this mediation and litigation, but such outcomes will have a significant impact on bondholders of those municipal securities. Further legislation by the U.S. Congress, or actions by the oversight board established by PROMESA, or court approval of an unfavorable debt restructuring deal could have a negative impact on the marketability, liquidity or value of certain investments held by the Fund and could reduce the Fund’s performance. These challenges and uncertainties have been exacerbated by Hurricanes Irma and Maria and the resulting natural disasters in Puerto Rico since 2017. In September 2017, Hurricanes Irma and Maria struck Puerto Rico, causing major damage across the Commonwealth, including damage to its water, power, and telecommunications infrastructure. The length of time needed to rebuild Puerto Rico’s infrastructure is unclear, but could amount to years, during which the commonwealth is likely to be in an uncertain economic state. The full extent of the natural disasters’ impact on Puerto Rico’s economy and foreign investment in Puerto Rico is difficult to estimate. More recently, in late December 2019 and January 2020, a series of earthquakes hit Puerto Rico, including a magnitude 6.4 earthquake, the most powerful earthquake to hit the island in more than a century, causing an estimated $200 million in damage. In addition, in early 2020, as the population of Puerto Rico worked to recover from these natural disasters, the island was significantly impacted by Covid, resulting in the Commonwealth’s authorization of a $787 million relief package to fight the pandemic and its economic impacts. Any reduction in the Commonwealth’s, revenues as a result of the pandemic could have a negative ability on the Commonwealth to meet its debt service obligations, including with respect to debt held by the Fund. Puerto Rico’s political and economic conditions could have a negative impact on the liquidity or value of Puerto Rican municipal securities, and consequently may affect the Fund’s investments and its performance if the Fund invests a significant portion of its assets in Puerto Rican municipal securities. |  |  |  |  |  |  |  |
Reinvestment Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called municipal securities at market interest rates that are below the portfolio’s current earnings rate. A decline in income could affect the common shares’ market price, NAV and/or a common shareholder’s overall returns. |  |  |  |  |  |  |  |
Restricted and Illiquid Investments Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Restricted and Illiquid Investments Risk. Illiquid investments are investments that are not readily marketable. These investments may include restricted investments, including Rule 144A securities, which cannot be resold to the public without an effective registration statement under the 1933 Act, or, if they are unregistered, may be sold only in a privately negotiated transaction or pursuant to an available exemption from registration. The Fund may not be able to readily dispose of such investments at prices that approximate those at which the Fund could sell such investments if they were more widely traded and, as a result of such illiquidity, the Fund may have to sell other investments or engage in borrowing transactions if necessary to raise cash to meet its obligations. Limited liquidity can also affect the market price of investments, thereby adversely affecting the Fund’s NAV and ability to make dividend distributions. The financial markets in general have in recent years experienced periods of extreme secondary market supply and demand imbalance, resulting in a loss of liquidity during which market prices were suddenly and substantially below traditional measures of intrinsic value. During such periods, some investments could be sold only at arbitrary prices and with substantial losses. Periods of such market dislocation may occur again at any time. |  |  |  |  |  |  |  |
Special Considerations Related to Single State Concentration Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Special Considerations Related to Single State Concentration Risk. Because the Fund primarily invests in municipal securities from a single state, the Fund is more susceptible to political, economic or regulatory factors affecting issuers of single state municipal securities. Information regarding the financial condition of the state is ordinarily included in various public documents issued thereby, such as the official statements prepared in connection with the issuance of general obligation bonds for the state. Additionally, the states are party to numerous legal proceedings, many of which normally occur in governmental operations. The creditworthiness of obligations issued by local issuers of the state may be unrelated to the creditworthiness of obligations issued by the state, and that there is no obligation on the part of the state to make payment on such local obligations in the event of default. |  |  |  |  |  |  |  |
Special Risks Related to Certain Municipal Obligations [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Special Risks Related to Certain Municipal Obligations. Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non-appropriation” clauses that relieve the governmental issuer of any obligation to make future payments under the lease or contract unless money is appropriated for such purpose by the appropriate legislative body. In addition, such leases or contracts may be subject to the temporary abatement of payments in the event that the governmental issuer is prevented from maintaining occupancy of the leased premises or utilizing the leased equipment. Although the obligations may be secured by the leased equipment or facilities, the disposition of the property in the event of non-appropriation or foreclosure might prove difficult, time consuming and costly, and may result in a delay in recovering or the failure to fully recover the Fund’s original investment. In the event of non-appropriation, the issuer would be in default and taking ownership of the assets may be a remedy available to the Fund, although the Fund does not anticipate that such a remedy would normally be pursued. Certificates of participation involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificates of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation. |  |  |  |  |  |  |  |
Structured Products Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Structured Products Risk. In addition to the general risks associated with investments in debt securities, holders of structured products bear risks of the underlying investments, index or reference obligation (collectively, the “reference instrument”) and are subject to counterparty, valuation and liquidity risks. The Fund may have the right to receive payments to which it is entitled only from the structured product, and generally does not have direct rights against the issuer or the entity that sold assets to the special purpose trust. While certain structured products enable the investor to acquire interests in a pool of securities without the brokerage and other expenses associated with directly holding the same securities, investors in structured products generally pay their share of the structured product’s administrative and other expenses. When investing in structured products, it is impossible to predict whether the reference instrument will rise or fall, but prices of the reference instrument (and, therefore, the prices of structured products) will be influenced by the same types of political and economic events that affect particular issuers of securities and capital markets generally. Structured products may also be less liquid, more volatile and more difficult to price than other types of securities. |  |  |  |  |  |  |  |
Swap Transactions Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Swap Transactions Risk. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by the investment adviser and/or the sub-adviser of not only the referenced asset, rate or index, but also of the swap itself. If the investment adviser and/ or the sub-adviser is incorrect in its forecasts of default risks, market spreads or other applicable factors or events, the investment performance of the Fund would diminish compared with what it would have been if these techniques were not used. |  |  |  |  |  |  |  |
Tax Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Tax Risk. The value of the Fund’s investments and its NAV may be adversely affected by changes in tax rates, rules and policies. Additionally, the Fund is not a suitable investment for individual retirement accounts, for other tax exempt or tax-deferred accounts, for investors who are not sensitive to the federal income tax consequences of their investments. |  |  |  |  |  |  |  |
Taxability Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Taxability Risk. The Fund will invest in municipal securities in reliance at the time of purchase on an opinion of bond counsel to the issuer that the interest paid on those securities will be excludable from gross income for regular federal income tax purposes, and the sub-adviser will not independently verify that opinion. Subsequent to the Fund’s acquisition of such a municipal security, however, the security may be determined to pay, or to have paid, taxable income. As a result, the treatment of dividends previously paid or to be paid by the Fund as “exempt-interest dividends” could be adversely affected, subjecting the Fund’s shareholders to increased federal income tax liabilities. Certain other investments made by the Fund, including derivatives transactions, may result in the receipt of taxable income or gains by the Fund. |  |  |  |  |  |  |  |
Tobacco Settlement Bond Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Tobacco Settlement Bond Risk. Tobacco settlement bonds are municipal securities that are backed solely by expected revenues to be derived from lawsuits involving tobacco related deaths and illnesses which were settled between certain states and American tobacco companies. Tobacco settlement bonds are secured by an issuing state’s proportionate share in the Master Settlement Agreement, an agreement between 46 states and nearly all of the U.S. tobacco manufacturers (the “MSA”). Under the terms of the MSA, the actual amount of future settlement payments by tobacco-manufacturers is dependent on many factors, including, among other things, reduced cigarette consumption. Payments made by tobacco manufacturers could be negatively impacted if the decrease in tobacco consumption is significantly greater than the forecasted decline. |  |  |  |  |  |  |  |
Unrated Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Unrated Securities Risk. Unrated securities determined by the Fund’s investment adviser to be of comparable quality to rated investments which the Fund may purchase may pay a higher dividend or interest rate than such rated investments and be subject to a greater risk of illiquidity or price changes. Less public information is typically available about unrated investments or issuers than rated investments or issuers. Some unrated securities may not have an active trading market or may be difficult to value, which means the Fund might have difficulty selling them promptly at an acceptable price. To the extent that the Fund invests in unrated securities, the Fund’s ability to achieve its investment objectives will be more dependent on the investment adviser’s credit analysis than would be the case when the Fund invests in rated securities. |  |  |  |  |  |  |  |
Valuation Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Valuation Risk. The municipal securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including readily available market quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to sell a portfolio security at the price established by the pricing service, which could result in a loss to the Fund. Pricing services generally price municipal securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Different pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s NAV. |  |  |  |  |  |  |  |
When Issued and Delayed Delivery Transactions Risks [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | When-Issued and Delayed-Delivery Transactions Risk. When-issued and delayed-delivery transactions may involve an element of risk because no interest accrues on the securities prior to settlement and, because securities are subject to market fluctuations, the value of the securities at time of delivery may be less (or more) than their cost. A separate account of the Fund will be established with its custodian consisting of cash equivalents or liquid securities having a market value at all times at least equal to the amount of any delayed payment commitment. |  |  |  |  |  |  |  |
Zero Coupon Bonds Risk or Pay In Kind Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Zero Coupon Bonds Risk or Pay-In-Kind Securities Risk. Zero Coupon and pay-in-kind securities may be subject to greater fluctuation in value and less liquidity in the event of adverse market conditions than comparably rated securities paying cash interest at regular interest payment periods. Prices on non-cash-paying instruments may be more sensitive to changes in the issuer’s financial condition, fluctuation in interest rates and market demand/ supply imbalances than cash-paying securities with similar credit ratings, and thus may be more speculative. |  |  |  |  |  |  |  |
Anti Takeover Provisions Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Anti-Takeover Provisions. The Declaration of Trust and the Fund’s by-laws include provisions that could limit the ability of other entities or persons to acquire control of the Fund or convert the Fund to open-end status. These provisions could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares. |  |  |  |  |  |  |  |
Counterparty Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Counterparty Risk. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives or other transactions supported by another party’s credit will affect the value of those instruments. Certain entities that have served as counterparties in the markets for these transactions have incurred or may incur in the future significant financial hardships including bankruptcy and losses as a result of exposure to sub-prime mortgages and other lower-quality credit investments. As a result, such hardships have reduced these entities’ capital and called into question their continued ability to perform their obligations under such transactions. By using such derivatives or other transactions, the Fund assumes the risk that its counterparties could experience similar financial hardships. In the event of the insolvency of a counterparty, the Fund may sustain losses or be unable to liquidate a derivatives position. |  |  |  |  |  |  |  |
Cybersecurity Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Cybersecurity Risk. The Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund. |  |  |  |  |  |  |  |
Economic and Political Events Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Economic and Political Events Risk. The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the municipal securities of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the creditworthiness and value of such municipal securities. |  |  |  |  |  |  |  |
Fund Tax Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Fund Tax Risk. The Fund has elected to be treated and intends to qualify each year as a Regulated Investment Company (“RIC”) under the Internal Revenue Code of 1986, as amended (the “Code”). As a RIC, the Fund is not expected to be subject to U.S. federal income tax to the extent that it distributes its investment company taxable income and net capital gains. To qualify for the special tax treatment available to a RIC, the Fund must comply with certain investment, distribution, and diversification requirements. Under certain circumstances, the Fund may be forced to sell certain assets when it is not advantageous in order to meet these requirements, which may reduce the Fund’s overall return. If the Fund fails to meet any of these requirements, subject to the opportunity to cure such failures under applicable provisions of the Code, the Fund’s income would be subject to a double level of U.S. federal income tax. The Fund’s income, including its net capital gain, would first be subject to U.S. federal income tax at regular corporate rates, even if such income were distributed to shareholders and, second, all distributions by the Fund from earnings and profits, including distributions of net capital gain (if any), would be taxable to shareholders as dividends. |  |  |  |  |  |  |  |
Global Economic Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Global Economic Risk. National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and asset prices around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies, may have global negative economic and market repercussions. Additionally, instability in various countries, war, natural and environmental disasters, the spread of infectious illnesses or other public health emergencies, terrorist attacks in the United States and around the world, growing social and political discord in the United States, debt crises, the response of the international community—through economic sanctions and otherwise—to international events, further downgrade of U.S. government securities, changes in the U.S. president or political shifts in Congress, trade disputes and other similar events may adversely affect the global economy and the markets and issuers in which the Fund invests. These events could reduce consumer demand or economic output, result in market closure, travel restrictions or quarantines, and generally have a significant impact on the global economy. These events could also impair the information technology and other operational systems upon which the Fund’s service providers, including the Fund’s sub-adviser, rely, and could otherwise disrupt the ability of employees of the Fund’s service providers to perform essential tasks on behalf of the Fund. The Fund does not know and cannot predict how long the securities markets may be affected by these events, and the future impact of these and similar events on the global economy and securities markets is uncertain. The Fund may be adversely affected by abrogation of international agreements and national laws which have created the market instruments in which the Fund may invest, failure of the designated national and international authorities to enforce compliance with the same laws and agreements, failure of local, national and international organizations to carry out the duties prescribed to them under the relevant agreements, revisions of these laws and agreements which dilute their effectiveness or conflicting interpretation of provisions of the same laws and agreements. Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. |  |  |  |  |  |  |  |
Investment and Market Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Investment and Market Risk. An investment in common shares is subject to investment risk, including the possible loss of the entire principal amount that you invest. Common shares frequently trade at a discount to their NAV. An investment in common shares represents an indirect investment in the securities owned by the Fund. Common shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of Fund dividends and distributions. |  |  |  |  |  |  |  |
Legislation and Regulatory Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Legislation and Regulatory Risk. At any time after the date of this report, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, securities held by the Fund or the issuers of such securities. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objectives. |  |  |  |  |  |  |  |
Leverage Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Leverage Risk. The use of leverage creates special risks for common shareholders, including potential interest rate risks and the likelihood of greater volatility of NAV and market price of, and distributions on, the common shares. The use of leverage in a declining market will likely cause a greater decline in the Fund’s NAV, which may result at a greater decline of the common share price, than if the Fund were not to have used leverage. Certain types of leverage may result in the Fund being subject to certain covenants, asset coverage or other portfolio composition limits by its lenders, debt or preferred securities purchasers, rating agencies that may rate the debt or preferred securities, or reverse repurchase counterparties. Such limitations may be more stringent than those imposed by the 1940 Act and may impact whether the Fund is able to maintain its desired amount of leverage. In addition, whenever the Fund incurs borrowings and/or preferred shares are outstanding, Common Shareholders will not be entitled to receive any cash distributions from the Fund unless all interest on such borrowings has been paid and all accumulated dividends on preferred shares have been paid, unless asset coverage (as defined in the 1940 Act) with respect to any borrowings would be at least 300% after giving effect to the distributions and asset coverage (as defined in the 1940 Act) with respect to preferred shares would be at least 200% after giving effect to the distributions. The Fund will pay (and common shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the Fund’s NAV. The investment adviser may, based on its assessment of market conditions and composition of the Fund’s holdings, increase or decrease the amount of leverage. Such changes may impact the Fund’s distributions and the price of the common shares in the secondary market. There is no assurance that the Fund’s use of leverage will be successful. The Fund may seek to refinance its leverage over time, in the ordinary course, as current forms of leverage mature or it is otherwise desirable to refinance; however, the form that such leverage will take cannot be predicted at this time. If the Fund is unable to replace existing leverage on comparable terms, its costs of leverage will increase. Accordingly, there is no assurance that the use of leverage may result in a higher yield or return to common shareholders. The amount of fees paid to the investment adviser and the sub-adviser for investment advisory services will be higher if the Fund uses leverage because the fees will be calculated based on the Fund’s Managed Assets – this may create an incentive for the investment adviser and the sub- adviser to leverage the Fund or increase the Fund’s leverage. |  |  |  |  |  |  |  |
Market Discount from Net Asset Value [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Market Discount from Net Asset Value. Shares of closed-end investment companies like the Fund frequently trade at prices lower than their NAV. This characteristic is a risk separate and distinct from the risk that the Fund’s NAV could decrease as a result of investment activities. Whether investors will realize gains or losses upon the sale of the common shares will depend not upon the Fund’s NAV but entirely upon whether the market price of the common shares at the time of sale is above or below the investor’s purchase price for the common shares. Furthermore, management may have difficulty meeting the Fund’s investment objectives and managing its portfolio when the underlying securities are redeemed or sold during periods of market turmoil and as investors’ perceptions regarding closed-end funds or their underlying investments change. Because the market price of the common shares will be determined by factors such as relative supply of and demand for the common shares in the market, general market and economic circumstances, and other factors beyond the control of the Fund, the Fund cannot predict whether the common shares will trade at, below or above NAV. The common shares are designed primarily for long-term investors, and you should not view the Fund as a vehicle for short-term trading purposes. |  |  |  |  |  |  |  |
Recent Market Conditions [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Recent Market Conditions. Periods of unusually high financial market volatility and restrictive credit conditions, at times limited to a particular sector or geographic area, have occurred in the past and may be expected to recur in the future. Some countries, including the United States, have adopted or have signaled protectionist trade measures, including the imposition of tariffs, relaxation of the financial industry regulations that followed the financial crisis, and/or reductions to corporate taxes. The scope of these policy changes is still developing, but the equity and debt markets may react strongly to expectations of change, which could increase volatility, particularly if a resulting policy runs counter to the market’s expectations. The outcome of such changes cannot be foreseen at the present time. In addition, geopolitical and other risks, including environmental and public health risks, may add to instability in the world economy and markets generally. As a result of increasingly interconnected global economies and financial markets, the value and liquidity of the Fund’s investments may be negatively affected by events impacting a country or region, regardless of whether the Fund invests in issuers located in or with significant exposure to such country or region. Ukraine has experienced ongoing military conflict, most recently commencing in February 2022 when Russia invaded Ukraine; this conflict may expand and military attacks could occur elsewhere in Europe. Europe has also been struggling with mass migration from the Middle East and Africa. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. Additionally, in October 2023 armed conflict broke out between Israel and the militant group Hamas after Hamas infiltrated Israel’s southern border from the Gaza Strip. Israel has since declared war against Hamas and this conflict has escalated into a greater regional conflict. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. The ongoing trade war between China and the United States, including the imposition of tariffs by each country on the other country’s products, has created a tense political environment. These actions may trigger a significant reduction in international trade, adverse effects in the supply of certain manufactured goods, substantial adverse price changes for goods and possible failure of individual companies and/or large segments of China’s export industry and U.S. importers, which could have a negative impact on the Fund’s performance. U.S. companies that source material and goods from China and those that make large amounts of sales in China are particularly vulnerable to an escalation of trade tensions. Beginning in early 2025, the United States also imposed tariffs on other countries, including Mexico and Canada. The possibility of additional tariffs being imposed or the outbreak of a trade war may adversely impact U.S. and international markets. Uncertainty regarding the outcome of the trade tensions and the potential for a trade war could cause the U.S. dollar to decline further. Events such as these and their consequences are difficult to predict and it is unclear whether further tariffs may be imposed or other escalating actions may be taken in the future. Additionally, political uncertainty regarding U.S. policy, including the U.S. government’s approach to trade, may impact the markets and the Fund’s performance. The U.S. Federal Reserve (the “Fed”) has in the past sharply raised interest rates, and has signaled an intention to maintain relatively higher interest rates until current inflation levels re-align with the Fed’s long-term inflation target. Changing interest rate environments impact the various sectors of the economy in different ways. For example, in March 2023, the Federal Deposit Insurance Corporation (“FDIC”) was appointed receiver for each of Silicon Valley Bank and Signature Bank, the second- and third-largest bank failures in U.S. history, which failures may be attributable, in part, to rising interest rates. Bank failures may have a destabilizing impact on the broader banking industry or markets generally. The impact of these developments in the near- and long-term is unknown and could have additional adverse effects on economies, financial markets and asset valuations around the world. |  |  |  |  |  |  |  |
Reverse Repurchase Agreement Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  |  |  |  |  |  |  |  | Reverse Repurchase Agreement Risk. A reverse repurchase agreement, in economic essence, constitutes a securitized borrowing by the Fund from the security purchaser. The Fund may enter into reverse repurchase agreements for the purpose of creating a leveraged investment exposure and, as such, their usage involves essentially the same risks associated with a leveraging strategy generally since the proceeds from these agreements may be invested in additional portfolio securities. Reverse repurchase agreements tend to be short-term in tenor, and there can be no assurances that the purchaser (lender) will commit to extend or “roll” a given agreement upon its agreed-upon repurchase date or an alternative purchaser can be identified on similar terms. Reverse repurchase agreements also involve the risk that the purchaser fails to return the securities as agreed upon, files for bankruptcy or becomes insolvent. The Fund may be restricted from taking normal portfolio actions during such time, could be subject to loss to the extent that the proceeds of the agreement are less than the value of securities subject to the agreement and may experience adverse tax consequences. |  |  |  |  |  |  |  |
Common Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other Annual Expenses [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis of Transaction Fees, Note [Text Block] |  |  |  |  |  |  |  |  |  |  | As a Percentage of Net Assets Attributableto Common Shares |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lowest Price or Bid |  | $ 11.51 | $ 11.45 | $ 11.28 | $ 11.54 | $ 10.68 | $ 10.55 | $ 10.57 |  | $ 9.26 |  |  |  |  |  |  |  |  |
Highest Price or Bid |  | 11.90 | 13.44 | 12.70 | 12.29 | 11.77 | 11.05 | 10.94 |  | 10.47 |  |  |  |  |  |  |  |  |
Lowest Price or Bid, NAV |  | 11.22 | 11.20 | 12.09 | 12.35 | 12.33 | 12.33 | 12.39 |  | 11.20 |  |  |  |  |  |  |  |  |
Highest Price or Bid, NAV |  | $ 11.07 | $ 12.16 | $ 12.17 | $ 12.49 | $ 12.73 | $ 12.76 | $ 12.63 |  | $ 12.36 |  |  |  |  |  |  |  |  |
Highest Price or Bid, Premium (Discount) to NAV [Percent] |  | 7.50% | 10.53% | 4.35% | (1.60%) | (7.54%) | (13.40%) | (13.38%) |  | (15.29%) |  |  |  |  |  |  |  |  |
Lowest Price or Bid, Premium (Discount) to NAV [Percent] |  | 2.58% | 2.23% | (6.70%) | (6.56%) | (13.38%) | (14.44%) | (14.69%) |  | (17.32%) |  |  |  |  |  |  |  |  |
Share Price |  | $ 11.86 |  |  |  |  |  |  |  |  | $ 11.86 |  |  |  |  |  |  |  |
NAV Per Share |  | $ 11.12 |  |  |  |  |  |  |  |  | $ 11.12 |  |  |  |  |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding Security, Title [Text Block] |  |  |  |  |  |  |  |  |  |  | Common shares |  |  |  |  |  |  |  |
Outstanding Security, Held [Shares] |  |  |  |  |  |  |  |  |  |  | 12,097,770 |  |  |  |  |  |  |  |
Adjustable Rate MuniFund Term Preferred Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial Highlights [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Securities Amount | [6] | $ 88,300,000 |  |  |  | $ 88,300,000 |  | $ 88,300,000 | [7] |  | $ 88,300,000 | $ 88,300,000 | $ 88,300,000 | $ 88,300,000 | $ 88,300,000 | $ 88,300,000 | $ 0 | $ 0 | $ 0
Senior Securities Coverage per Unit | [8] | $ 252,413 |  |  |  | $ 266,396 |  | $ 265,542 | [7] |  | $ 252,413 | $ 261,963 | $ 290,229 | $ 297,509 | $ 303,878 | $ 285,822 | $ 0 | $ 0 | $ 0
Variable Rate MuniFund Term Preferred Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial Highlights [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Securities Amount | [6] | $ 0 |  |  |  | $ 0 |  | $ 0 | [7] |  | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 88,300,000 | $ 88,300,000 | $ 79,000,000
Senior Securities Coverage per Unit | [8] | $ 0 |  |  |  | $ 0 |  | $ 0 | [7] |  | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 286,891 | $ 287,022 | $ 319,959
[1] | The maximum sales charge for offerings made at-the-market is 1.00%. If the Common Shares are sold to or through underwriters in an offering that is not made at-the-market, the applicable Prospectus Supplement will set forth any other applicable sales load. Additionally, the applicable Prospectus Supplement will set forth the offering expenses (if any) borne by Fund common shareholders.
[2] | You will be charged a $2.50 service charge and pay brokerage charges if you direct Computershare Inc. and Computershare Trust Company, N.A., as agent for the common shareholders, to sell your Common Shares held in a dividend reinvestment account.
[3] | Stated as percentages of average net assets attributable to Common Shares for the fiscal year ended August 31, 2025.
[4] | Interest and Other Related Expenses reflect actual expenses and fees for leverage incurred by a Fund for the fiscal year ended August 31, 2025. The types of leverage used by the Fund during the fiscal year ended August 31, 2025 are described in the Fund Leverage and the Notes to Financial Statements sections of this annual report. Actual Interest and Other Related Expenses incurred in the future may be higher or lower. If short-term market interest rates rise in the future, and if the Fund continues to maintain leverage, the cost of which is tied to short-term interest rates, the Fund’s interest expenses on its short-term borrowings can be expected to rise in tandem. The Fund’s use of leverage will increase the amount of management fees paid to the Fund’s adviser and sub-advisor(s).
[5] | Other Expenses are based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%.
[6] | Aggregate Amount Outstanding: Aggregate amount outstanding represents the principal amount outstanding or liquidation preference, if applicable, as of the end of the relevant fiscal year and does not include any preferred shares noticed for redemption as noted on the Statement of Assets and Liabilities, if applicable.
[7] | For the six months ended August 31, 2024. Prior to March 1, 2024, the Fund’s fiscal year end was February 29th.
[8] | Asset Coverage Per $100,000: Asset coverage per $100,000 is calculated by subtracting the Fund’s liabilities and indebtedness not represented by senior securities from the Fund’s total assets, dividing the result by the aggregate of the involuntary liquidation preference of the outstanding preferred shares and multiplying the result by 100,000. For purpose of asset coverage above, senior securities consist of preferred shares or borrowings (excluding temporary borrowings) of a Fund and does not include derivative transactions and other investments that have the economic effect of leverage such as reverse repurchase agreements and tender option bonds. If the leverage effects of such investments were included, the asset coverage amounts presented would be lower.

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