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N-2 - USD ($) $ / shares in Units, $ in Thousands |  | 6 Months Ended |  |  |  |  |  |  |  |  |  |
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May 31, 2023 | May 31, 2023 | Apr. 28, 2023 | Mar. 31, 2023 | Feb. 28, 2023 | Jan. 31, 2023 | Dec. 30, 2022 | Nov. 30, 2022 | Nov. 30, 2021 | Nov. 30, 2020 | Nov. 30, 2019 | Nov. 30, 2018
Cover [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Entity Central Index Key |  |  |  | 0000882071 |  |  |  |  |  |  |  |  |  |  |
Amendment Flag |  |  |  | false |  |  |  |  |  |  |  |  |  |  |
Document Type |  |  |  | N-CSRS |  |  |  |  |  |  |  |  |  |  |
Entity Registrant Name |  |  |  | Flaherty & Crumrine Preferred and Income Opportunity Fund Incorporated |  |  |  |  |  |  |  |  |  |  |
Financial Highlights [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Securities [Table Text Block] |  |  |  | Senior Securities
|  | 5/31/2023* |  | 11/30/2022 |  | 11/30/2021 |  | 11/30/2020 |  | 11/30/2019 |  | 11/30/2018 | ​
Total Debt Outstanding, End of Period (000s)(1) | ​ | $80,600​ | ​ | $80,600​ | ​ | $80,600​ | ​ | $74,700​ | ​ | $74,700​ | ​ | $74,700​ | ​
Asset Coverage per $1,000 of Debt(2) | ​ | 2,405 | ​ | 2,525 | ​ | 2,944 | ​ | 3,037 | ​ | 3,008 | ​ | 2,770 | ​
* |  | Unaudited
(1) |  | See Note 7.
(2) |  | Calculated by subtracting the Fund’s total liabilities (excluding the loan) from the Fund’s total assets and dividing that amount by the loan outstanding in 000’s.
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment Objectives and Practices [Text Block] |  |  |  | Investment Objective and Policies The Fund’s investment objective is to provide its common shareholders with high current income consistent with preservation of capital. The Fund’s investment objective may not be changed except through an amendment to the Fund’s Articles of Incorporation. Any such amendment would require the affirmative vote of at least 80% of the votes of the Fund’s Common Shares and preferred stock (“Preferred Shares”) entitled to be cast by shareholders, voting together as a single class, and of at least 80% of the votes of the Fund’s Preferred Shares entitled to be cast by shareholders, voting as a separate class; unless such change in investment objective has been approved by the affirmative vote of 80% of the total number of directors of the Fund, in which case only the affirmative vote of a majority of the Common Shares and Preferred Shares entitled to vote, voting together as a single class, is required to approve such amendment. The Fund’s investment policies may be changed by the Fund’s Board of Directors without shareholder approval. However, the Fund’s 80% investment policy described below may only be changed upon 60 days’ prior written notice to the Fund’s shareholders. Under normal market conditions, the Fund invests at least 80% of its Managed Assets (defined below) in a portfolio of preferred and other income-producing securities. Preferred and other income-producing securities may include, among other things, traditional preferred stock, trust preferred securities, hybrid securities that have characteristics of both equity and debt securities, contingent capital securities (“CoCos”), subordinated debt and senior debt. “Managed Assets” are the Fund’s net assets, plus the principal amount of loans from financial institutions or debt securities issued by the Fund, the liquidation preference of preferred stock issued by the Fund, if any, and the proceeds of any reverse repurchase agreements entered into by the Fund. The Fund will invest, under normal market conditions, at least 25% of its total assets in companies principally engaged in the financial services sector. For purposes of this policy, a company is “principally engaged” in financial services if it derives at least 50% of its revenue from providing financial services. Companies in the financial services sector include: commercial banks, industrial banks, savings institutions, finance companies, diversified financial services companies, investment banking firms, securities brokerage houses, investment advisory companies, leasing companies, insurance companies and companies providing similar services. In addition, the Fund also may focus its investments in other sectors or industries, such as (but not limited to) energy, industrials, utilities, communications and pipelines. The Adviser retains broad discretion to allocate the Fund’s investments as it deems appropriate considering current market and credit conditions. The Fund may invest up to 100% of its total assets in securities of U.S. companies, and may also invest up to 30% of its total assets in U.S. dollar-denominated securities issued by companies organized or having their principal place of business outside the United States. At the time of purchase, at least 85% of the Fund’s total assets will be either (a) rated investment grade by any one of Moody’s Investors Service, Inc. (“Moody’s”), S&P Global Ratings (“S&P”) or Fitch Ratings (“Fitch”) or (b) issued by companies with issuer or senior unsecured debt ratings that are investment grade by any one of Moody’s, S&P or Fitch. In addition, for purposes of this 85% policy, the Fund may include unrated securities that the Adviser deems to be comparable in quality to rated issues in which the Fund is authorized to invest. Some of the Fund’s total assets may be invested in securities rated (or issued by companies rated) below investment grade at the time of purchase. Securities that are rated below investment grade are commonly referred to as “high yield” or “junk bonds.” Securities of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay dividends and interest and repayment of principal. Due to the risks involved in investing in securities of below investment grade quality, an investment in the Fund should be considered speculative. The maturities of securities in which the Fund will invest generally will be longer-term (perpetual, in the case of many preferred securities and CoCos, and ten years or more for other preferred and debt securities); however, as a result of changing market conditions and interest rates, the Fund may also invest in shorter-term securities. The Fund can buy securities of any maturity or duration. 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 than securities with shorter durations. For example, a three-year duration means a bond is expected to decrease in value by 3% if interest rates rise by 1% and increase in value by 3% if interest rates fall by 1%. The portion of the Fund’s Managed Assets not invested in preferred and other income-producing securities may be invested in, among other securities, common stocks, money market instruments, money market mutual funds, asset- backed securities, and securities issued or guaranteed by the U.S. Government, its agencies or instrumentalities (“Government Securities”) and such obligations which are subject to repurchase agreements and commercial paper. Depending on market conditions, these investments may at times have a higher or lower yield than preferred securities and other income-producing securities in which the Fund invests. Unless designated as a “fundamental” policy or restriction and except as described above, the investment limitations and policies of the Fund may be changed by the Board of Directors without shareholder approval. Primary Investment Strategies and Techniques Preferred Securities. Preferred securities share many investment characteristics with both bonds and common stock; therefore, the risks and potential rewards of investing in the Fund may at times be similar to the risks of investing in equity-income funds or both equity funds and bond funds. Similar to bonds, preferred securities, which generally pay fixed- or adjustable-rate dividends or interest to investors, have preference over common stock in the payment of dividends or interest and the liquidation of a company’s assets, which means that a company typically must pay dividends or interest on its preferred securities before paying any dividends on its common stock. On the other hand, like common stock, preferred securities are junior to all forms of the company’s debt, including both senior and subordinated debt, and the company can skip or defer dividend or interest payments for extended periods of time without triggering an event of default. Further, different types of preferred securities can be junior or senior to other types of preferred securities in both priority of payment of dividends or interest and/or the liquidation of a company’s assets. Preferred securities can be structured differently for retail and institutional investors, and the Fund may purchase either structure. The retail segment is typified by $25 par securities that are listed on a stock exchange and which trade and are quoted with accreted dividend or interest income included in the price. The institutional segment is typified by $1,000 par value securities that are not exchange-listed, trade over-the-counter (“OTC”) and are quoted on a “clean” price, i.e., without accrued dividend or interest income included in the price. While preferred securities can be issued with a final maturity date, others (including most traditional preferred stock) are perpetual in nature. In certain instances, a final maturity date may be extended and/or the final payment of principal may be deferred at the issuer’s option for a specified time without any adverse consequence to the issuer. No redemption can typically take place unless all cumulative payment obligations to preferred security investors have been met, although issuers may be able to engage in open-market repurchases without regard to any cumulative dividends or interest payable, and many preferred securities are non-cumulative, whereby the issuer does not have an obligation to make up any arrearages to holders of such securities. Debt Securities. The Fund may invest in a variety of debt securities, including corporate senior or subordinated debt securities and U.S. government securities. Corporate debt securities are fixed-income securities issued by businesses to finance their operations. The issuer pays the investor a fixed or variable rate of interest and normally must repay the amount borrowed on or before maturity. Notes, bonds, debentures and commercial paper are the most common types of corporate debt securities, with the primary difference being their maturities and secured or unsecured status. Contingent Capital Securities. Contingent capital securities or “CoCos” have features similar to preferred and other income producing securities but also include “loss absorption” or mandatory conversion provisions that make the securities more like equity. An automatic write-down or conversion event is typically triggered by a reduction in the capital level of the issuer, but may also be triggered by regulatory actions (e.g., a change in capital requirements) or by other factors. Illiquid Securities. The Fund may invest without limit in instruments that lack a secondary trading market or are otherwise considered illiquid. Generally, illiquid securities are securities that cannot be disposed of within seven days in the ordinary course of business at approximately the value at which the Fund has valued the securities. Fundamental Investment Restrictions. The Fund has adopted certain fundamental investment restrictions that may not be changed without the approval of the holders of a majority of the outstanding voting securities, voting together as a single class, and of the holders of a majority of the outstanding Preferred Shares voting as a separate class. A “majority of the outstanding voting securities” for this purpose means the lesser of (1) 67% or more of the Common Shares and, if issued, preferred stock (“Preferred Shares”) present at a meeting of the shareholders, voting together as single class, if the holders of more than 50% of such shares are present or represented by proxy at the meeting, or (2) more than 50% of the outstanding Common Shares and outstanding Preferred Shares, voting together as a single class. A majority of the Fund’s outstanding Preferred Shares for this purpose is more than half of the outstanding Preferred Shares. For purposes of the restrictions listed below, all percentage limitations apply immediately after acquisition, and any subsequent change in any applicable percentage resulting from market fluctuations does not require elimination or reduction of any security from the Fund’s portfolio. Under its fundamental restrictions: 1. The Fund may not purchase securities (other than Government Securities) of any issuer if as a result of the purchase more than 5% of the value of the Fund’s total assets would be invested in the securities of that issuer, except that up to 25% of the value of the Fund’s total assets may be invested without regard to this 5% limitation. 2.The Fund may not purchase more than 10% of the voting securities of any one issuer, or more than 10% of the securities of any class of any one issuer, except that (i) this limitation is not applicable to the Fund’s investments in Government Securities and (ii) up to 25% of the value of the Fund’s total assets may be invested without regard to this 10% limitation. 3.The Fund may not borrow money, except as permitted under the 1940 Act, as amended, and as interpreted or modified by regulatory authority having jurisdiction, from time to time. 4.The Fund may not sell securities short or purchase securities on margin, except as permitted under the 1940 Act, as amended, and as interpreted or modified by regulatory authority having jurisdiction, from time to time. 5.The Fund may not underwrite any issue of securities, except to the extent that the sale of portfolio securities may be deemed to be an underwriting. 6.The Fund may not purchase, hold or deal in real estate or oil and gas interests, except that the Fund may invest in securities secured by real estate or interests in real estate. 7.The Fund may purchase and sell commodities or commodity contracts, including futures contracts, to the extent permitted by law. 8.The Fund may not lend any funds or other assets, except through purchasing debt securities, lending portfolio securities and entering into repurchase agreements consistent with the Fund’s investment objective. 9.The Fund may not issue senior securities to the extent such issuance would violate applicable law. 10.The Fund may not invest more than 25% of its total assets in securities of issuers in a single industry, except that this limitation will not be applicable to the purchase of Government Securities, provided that the Fund will invest at least 25% of its total assets in the financial services sector. 11.The Fund may not make any investments for the purpose of exercising control or management of any company. Except for the investment restrictions set forth above, the Fund’s investment objective and the Fund’s policy of concentrating in the financial services sector, the other policies and percentage limitations referred to in the Prospectus or in this SAI are not fundamental policies of the Fund and, unless provided to the contrary in the Fund’s Articles of Incorporation (together with any amendments or supplements thereto, including any articles supplementary, the “Articles of Incorporation”), may be changed by the Fund’s Board of Directors without shareholder approval. In addition, (1) the Fund’s investment objective, (2) the Fund’s status as a diversified investment company (the requirements for which are embodied in investment restrictions nos. 1 and 2 above) and (3) the Fund’s policy of not making any investments for the purpose of exercising control or management of any company (see investment restriction no. 11 above) may not be changed except through an amendment to the Fund’s Articles of Incorporation. Any such amendment would require the affirmative vote of at least 80% of the votes of the Common Shares and Preferred Shares entitled to be cast by shareholders, voting together as a single class, and of at least 80% of the votes of the Preferred Shares entitled to be cast by shareholders, voting as a separate class; unless such change in investment objective has been approved by the affirmative vote of 80% of the total number of directors of the Fund, in which case only the affirmative vote of a majority of the Common Shares and Preferred Shares entitled to vote, voting together as a single class, is required to approve such amendment. The Fund’s 80% investment policy is non-fundamental and may be changed by the Board of Directors without shareholder approval, to become effective on at least 60 days’ written notice to shareholders prior to any such change. With respect to investment restriction number 10, the Fund, for example, could have more than 25% of its total assets in insurance companies, while at other times it could have that portion invested in banks. At all times, though, the Fund would have at least 25% of its total assets invested in the financials services sector. In addition, the Fund also may focus its investments in other sectors or industries, such as (but not limited to) energy, industrials, utilities, and pipelines. The Adviser retains broad discretion to allocate the Fund’s investments as it deems appropriate in light of current market and credit conditions. |  |  |  |  |  |  |  |  |  |  |
Risk Factors [Table Text Block] |  |  |  | Principal Risks of the Fund The Fund is a diversified, closed-end management investment company designed primarily as a long-term investment and not as a trading vehicle. The Fund is not intended to be a complete investment program and, due to the uncertainty inherent in all investments, there can be no assurance that the Fund will achieve its investment objective. Different risks may be more significant at different times depending on market conditions. Market Events Risk. Market disruption can be caused by economic, financial or political events and factors, including but not limited to, international wars or conflicts (including Russia’s military invasion of Ukraine), geopolitical developments (including trading and tariff arrangements, sanctions and cybersecurity attacks), instability in regions such as Asia, Eastern Europe and the Middle East, terrorism, natural disasters and public health epidemics (including the outbreak of COVID-19 globally). The extent and duration of such events and resulting market disruptions cannot be predicted, but could be substantial and could magnify the impact of other risks to the Fund. These and other similar events could adversely affect the U.S. and foreign financial markets and lead to increased market volatility, reduced liquidity in the securities markets, significant negative impacts on issuers and the markets for certain securities and commodities and/or government intervention. They may also cause short- or long-term economic uncertainties in the United States and worldwide. As a result, whether or not the Fund invests in securities of issuers located in or with significant exposure to the countries directly affected, the value and liquidity of the Fund’s investments may be negatively impacted. Preferred, Contingent Capital and Other Subordinated Securities Risk. Preferred, contingent capital and other subordinated securities rank lower than bonds and other debt instruments in a company’s capital structure and therefore are subject to greater credit risk than those debt instruments. Distributions on some types of these securities may also be skipped or deferred by issuers without causing a default. Finally, some of these securities typically have special redemption rights that allow the issuer to redeem the security at par earlier than scheduled. If this occurs, the Fund may be forced to reinvest in lower yielding securities. Contingent Capital Securities Risk. Contingent capital securities or “CoCos” have features and risks similar to preferred and other income producing securities but also include “loss absorption” or mandatory conversion provisions and restrictions on dividend or interest payments that make the securities more like equity. This is particularly true in the financial sector, the largest preferred issuer segment. In one version of a CoCo, the security has loss absorption characteristics whereby the liquidation value of the security may be adjusted downward to below the original par value (even to zero) under certain circumstances. This may occur, for instance, in the event that business losses have eroded capital to a substantial extent. The write down of the par value would occur automatically and would not entitle the holders to seek bankruptcy of the company. In addition, an automatic write-down could result in a reduced income rate if the dividend or interest payment is based on the security’s par value. Such securities may, but are not required to, provide for circumstances under which the liquidation value may be adjusted back up to par, such as an improvement in capitalization and/or earnings. Another version of a CoCo provides for mandatory conversion of the security into common shares of the issuer under certain circumstances. The mandatory conversion might relate, for instance, to maintenance of a capital minimum, whereby falling below the minimum would trigger automatic conversion. Since the common stock of the issuer may not pay a dividend, investors in these instruments could experience a reduced income rate, potentially to zero, and conversion would deepen the subordination of the investor, hence worsening the Fund’s standing in a bankruptcy. In addition, some such instruments also provide for an automatic write-down if the price of the common stock is below the conversion price on the conversion date. An automatic write-down or conversion event is typically triggered by a reduction in the capital level of the issuer, but may also be triggered by regulatory actions (e.g., a change in capital requirements) or by other factors. In addition, interest or dividend payments may be reduced or eliminated if certain earnings or capital levels are breached. Trust Preferred Securities Risk. Some preferred securities are issued by trusts or other special purpose entities established by operating companies and are not a direct obligation of an operating company. In some cases, when investing in hybrid-preferred securities issued by trusts or other special purpose entities, the Fund may not have recourse against the operating company in the event that the trust or other special purpose entity cannot pay the obligation and therefore, the Fund may lose some or all of the value of its investments in the hybrid-preferred security. Concentration Risk. The Fund invests at least 25% of its total assets in the financial services sector. This policy makes the Fund more susceptible to adverse economic or regulatory occurrences affecting the financial services sector. Financial Services Sector Risk. The financial services sector is especially subject to the adverse effects of economic recession, currency exchange rates, government regulation, decreases in the availability of capital, volatile interest rates, portfolio concentrations in geographic markets and in commercial and residential real estate loans, and competition from new entrants in their fields of business. U.S. and foreign laws and regulations require banks and bank holding companies to maintain minimum levels of capital and liquidity and to establish loan loss reserves. A bank’s failure to maintain specified capital ratios may trigger dividend restrictions, suspensions on payments on subordinated debt, preferred securities and contingent capital securities, and limitations on growth. Bank regulators have broad authority in these instances and can ultimately impose sanctions, such as imposing resolution authority, conservatorship or receivership, on such non-complying banks even when these banks continue to be solvent, thereby possibly resulting in the elimination of stockholders’ equity. Unless a bank holding company has subsidiaries other than banks that generate substantial revenues, the holding company’s cash flow and ability to declare dividends may be impaired severely by restrictions on the ability of its bank subsidiaries to declare dividends or ultimately to redeem its securities (as they mature). Similarly, U.S. and foreign laws and regulations require insurance companies to maintain minimum levels of capital and liquidity. An insurance company’s failure to maintain these capital ratios may also trigger dividend restrictions, suspensions on payments of subordinated debt, and limitations on growth. Insurance regulators (at the state-level in the United States) have broad authority in these instances and can ultimately impose sanctions, including conservatorship or receivership, on such non-complying insurance companies even when these companies continue to be solvent, thereby possibly resulting in the elimination of shareholders’ equity. In addition, insurance regulators have extensive authority in some categories of insurance of approving premium levels and setting required levels of underwriting. Companies engaged in stock brokerage, commodity brokerage, investment banking, investment management or related investment advisory services are closely tied economically to the securities and commodities markets and can suffer during a decline in either market. These companies also are subject to the regulatory environment and changes in regulations, pricing pressure, the availability of funds to borrow and interest rates. Credit Risk. Credit risk is the risk that an issuer of a security will be unable or unwilling to make dividend, interest and principal payments when due and the related risk that the value of a security may decline because of concerns about the issuer’s ability to make such payments. Credit risk may be heightened for the Fund because the Fund may invest in “high yield” or “high risk” securities; such securities, while generally offering higher yields than investment grade securities with similar maturities, involve greater risks, including the possibility of default or bankruptcy, and are regarded as predominantly speculative with respect to the issuer’s capacity to pay dividends and interest and repay principal. High Yield Securities Risk. Although high yield securities generally pay higher rates of interest than investment grade securities, high yield securities are high-risk investments that may cause income and principal losses for the Fund. High yield securities may be issued by less creditworthy issuers. Issuers of high yield securities may have a larger amount of outstanding debt relative to their assets than issuers of investment grade securities. In the event of an issuer’s bankruptcy, claims of other creditors may have priority over the claims of high yield bond holders, for example, leaving few or no assets available to repay high yield bond holders. Prices of high yield securities are subject to extreme price fluctuations. Adverse changes in an issuer’s industry and general economic conditions may have a greater impact on the prices of high yield securities than on other higher rated fixed-income securities. Issuers of high yield securities may be unable to meet their interest or principal payment obligations because of an economic downturn, specific issuer developments, or the unavailability of additional financing. High yield securities frequently have redemption features that permit an issuer to repurchase the security from the Fund before it matures. If the issuer redeems high yield securities, the Fund may have to invest the proceeds in securities with lower yields and may lose income. High yield securities may be less liquid than higher rated fixed-income securities, even under normal economic conditions. There may be significant differences in the prices quoted for high yield securities by dealers in the market. Because they are less liquid, judgment may play a greater role in valuing certain of the Fund’s securities than is the case with securities trading in a more liquid market. The Fund may incur expenses to the extent necessary to seek recovery upon default or to negotiate new terms with a defaulting issuer. The credit rating of a high yield security does not necessarily address its market value risk. Ratings and market value may change from time to time, positively or negatively, to reflect new developments regarding the issuer. Credit Agency Risk. Credit ratings are determined by credit rating agencies and are the opinions of such entities. A rating assigned by a rating agency is not an absolute standard of credit quality and does not evaluate a security’s market risk or liquidity. Any shortcomings or inefficiencies in credit rating agencies’ processes for determining credit ratings may adversely affect the credit ratings of securities held by the Fund and, as a result, may adversely affect those securities’ perceived or actual credit risk. Interest Rate and Duration Risk. Interest rate risk is the risk that securities will decline in value because of changes in market interest rates. For fixed rate securities, when market interest rates rise, the market value of such securities generally will fall. Investments in fixed rate securities with long-term maturities may experience significant price declines if long-term interest rates increase. During periods of rising interest rates, the average life of certain types of securities may be extended because of slower than expected redemptions or prepayments. This may lock in a below- market yield, increase the security’s sensitivity to changes in interest rates (“duration”) and further reduce the value of the security. Fixed rate securities with longer durations tend to be more volatile than securities with shorter durations. The duration of a security will be expected to change over time with changes in market factors and time to maturity. The market value of floating-rate and fixed-to-floating rate 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 interest rate reset. A secondary risk associated with declining interest rates is the risk that income earned by the Fund on floating-rate and fixed-to-floating rate securities may decline due to lower coupon payments on floating-rate securities. Liquidity Risk. The Fund may invest, without limit, in illiquid securities. From time to time, certain securities held by the Fund may have limited marketability and may be difficult to sell at favorable times or prices. It is possible that certain securities held by the Fund will not be able to be sold in sufficient amounts or in a sufficiently timely manner to raise the cash necessary to meet the Fund’s obligations, including potential repayment of leverage borrowings, if any. Foreign Investment Risk. Because the Fund may invest its assets in foreign instruments, the value of Fund shares can be adversely affected by political and economic developments abroad. Foreign markets may be smaller, less liquid and more volatile than the major markets in the United States, and as a result, Fund share values may be more volatile. Trading in foreign markets typically involves higher expense than trading in the United States. The Fund may have difficulties enforcing its legal or contractual rights in a foreign country. Foreign legal systems generally have fewer regulatory requirements than the U.S. legal system, particularly those of emerging markets. In general, less information is publicly available with respect to non-U.S. companies than U.S. companies. Non-U.S. companies generally are not subject to the same accounting, auditing, and financial reporting standards as are U.S. companies. Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if the Fund invests proceeds from matured, traded or redeemed securities at market interest rates that are below the Fund portfolio’s current earnings rate. For example, during periods of declining interest rates, the issuer of a security may exercise its option to redeem a security, causing the Fund to reinvest the proceeds into lower-yielding securities, which may result in a decline in the Fund’s income and distributions to Common Shareholders. Selection Risk. Selection risk is the risk that the securities selected by Fund management will under-perform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. Management Risk. The Fund is an actively managed portfolio and its success depends upon the investment skills and analytical abilities of the Adviser to develop and effectively implement strategies that achieve the Fund’s investment objective. Decisions made by the Adviser may cause the Fund to incur losses or to miss profit opportunities. Leverage Risk. Leverage is a speculative technique and there are special risks and costs associated with leveraging. There is no assurance that leveraging strategy will be successful. Leverage involves risks and special considerations for holders of Common Shares, including: the likelihood of greater volatility of net asset value, market price and dividend rate of the Common Shares than a comparable portfolio without leverage; the risk that fluctuations in the interest or dividend rates that the Fund must pay on any leverage will reduce the return on the holders of the Common Shares; the effect of leverage in a declining market, which is likely to cause a greater decline in the net asset value of the Common Shares than if the Fund were not leveraged, which may result in a greater decline in the market price of the Common Shares; when the Fund uses financial leverage, the management fees payable to the Adviser will be higher than if the Fund did not use leverage; and leverage may increase operating costs, which may reduce total return. Risk of Market Price Discount from Net Asset Value. Shares of closed-end funds frequently trade at a discount from their net asset value. This characteristic is a risk separate and distinct from the risk that net asset value could decrease as a result of investment activities. We cannot predict whether the Common Shares will trade at, above or below net asset value. Valuation Risk. Unlike publicly traded common stock that trades on national exchanges, there is no central place or exchange for trading some of the preferred and other income securities owned by the Fund. Preferred, contingent capital and debt securities generally trade on an OTC market which may be anywhere in the world where the buyer and seller can settle on a price. Due to the lack of centralized information and trading, the valuation of these securities may carry more risk than that of common stock. Uncertainties in the conditions of the financial market, unreliable reference data, lack of transparency and inconsistency of valuation models and processes may lead to inaccurate asset pricing. Reference Rate Risk. The Fund may be exposed to debt securities, derivatives or other financial instruments that recently transitioned from the London Interbank Offered Rate, or “LIBOR,” as a “benchmark” or “reference rate” for various interest rate calculations. LIBOR’s administrator, ICE Benchmark Administration, ceased publishing most LIBOR settings (including some U.S. LIBOR settings) by the end of 2021 and the remaining (and most widely used) U.S. Dollar LIBOR settings after June 30, 2023. The United Kingdom Financial Conduct Authority, which regulates LIBOR, will permit the use of synthetic U.S. dollar LIBOR rates for non-U.S. contracts through September 30, 2024, but any such rates would be considered non-representative of the underlying market. Since 2018 the Federal Reserve Bank of New York has published the Secured Overnight Financing Rate (referred to as SOFR), which is intended to replace U.S. Dollar LIBOR. SOFR is a broad measure of the cost of borrowing cash overnight collateralized by U.S. Treasury securities in the repurchase agreement (repo) market. There is no assurance that the composition or characteristics of SOFR or any such alternative reference rate will be similar to or produce the same value or economic equivalence as LIBOR or that the market for SOFR-linked financial instruments will have the same volume or liquidity as did the market for LIBOR-linked financial instruments prior to LIBOR’s discontinuance or unavailability. Neither the long-term effect of the LIBOR transition process nor its ultimate success can yet be known. Cybersecurity Risk. Cybersecurity incidents, both intentional and unintentional, may allow an unauthorized party to gain access to Fund assets, Fund or customer data (including private shareholder information), or proprietary information, cause the Fund, the Adviser, and/or their service providers (including, but not limited to, fund accountants, custodians, sub-custodians, transfer agents and financial intermediaries) to suffer data breaches, data corruption or loss of operational functionality or prevent fund investors from purchasing, redeeming or exchanging shares or receiving distributions. The Fund and the Adviser have limited ability to prevent or mitigate cybersecurity incidents affecting third party service providers, and such third-party service providers may have limited indemnification obligations to the Fund or the Adviser. Cybersecurity incidents may result in financial losses to the Fund and its shareholders, and substantial costs may be incurred in order to prevent any future cybersecurity incidents. Issuers of securities in which the Fund invests are also subject to cybersecurity risks, and the value of these securities could decline if the issuers experience cybersecurity incidents. Given the risks described above, an investment in the Fund’s Common Shares may not be appropriate for all investors. You should carefully consider your ability to assume these risks before making an investment in the Fund. |  |  |  |  |  |  |  |  |  |  |
Share Price [Table Text Block] |  |  |  | Per Share of Common Stock
|  | Total Dividends Paid |  | Net Asset Value |  | NYSE Closing Price |  | Dividend Reinvestment Price(1) | ​
December 30, 2022 | ​ | $0.0555 | ​ | $ 9.22 | ​ | $8.60 | ​ | $8.93 | ​
January 31, 2023 | ​ | 0.0555 | ​ | 10.03 | ​ | 9.58 | ​ | 9.69 | ​
February 28, 2023 | ​ | 0.0500 | ​ | 9.80 | ​ | 9.14 | ​ | 9.16 | ​
March 31, 2023 | ​ | 0.0500 | ​ | 8.75 | ​ | 8.25 | ​ | 8.30 | ​
April 28, 2023 | ​ | 0.0500 | ​ | 8.85 | ​ | 8.06 | ​ | 8.11 | ​
May 31, 2023 | ​ | 0.0470 | ​ | 8.66 | ​ | 7.63 | ​ | 7.83 | ​
(1)Whenever the net asset value per share of the Fund’s Common Stock is less than or equal to the market price per share on the reinvestment date, new shares issued will be valued at the higher of net asset value or 95% of the then current market price. Otherwise, the reinvestment shares of Common Stock will be purchased in the open market. |  |  |  |  |  |  |  |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Document Period End Date |  |  |  | May 31, 2023 |  |  |  |  |  |  |  |  |  |  |
Trust Preferred Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Trust Preferred Securities Risk. Some preferred securities are issued by trusts or other special purpose entities established by operating companies and are not a direct obligation of an operating company. In some cases, when investing in hybrid-preferred securities issued by trusts or other special purpose entities, the Fund may not have recourse against the operating company in the event that the trust or other special purpose entity cannot pay the obligation and therefore, the Fund may lose some or all of the value of its investments in the hybrid-preferred security. |  |  |  |  |  |  |  |  |  |  |
Concentration Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Concentration Risk. The Fund invests at least 25% of its total assets in the financial services sector. This policy makes the Fund more susceptible to adverse economic or regulatory occurrences affecting the financial services sector. |  |  |  |  |  |  |  |  |  |  |
Financials Sector Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Financial Services Sector Risk. The financial services sector is especially subject to the adverse effects of economic recession, currency exchange rates, government regulation, decreases in the availability of capital, volatile interest rates, portfolio concentrations in geographic markets and in commercial and residential real estate loans, and competition from new entrants in their fields of business. U.S. and foreign laws and regulations require banks and bank holding companies to maintain minimum levels of capital and liquidity and to establish loan loss reserves. A bank’s failure to maintain specified capital ratios may trigger dividend restrictions, suspensions on payments on subordinated debt, preferred securities and contingent capital securities, and limitations on growth. Bank regulators have broad authority in these instances and can ultimately impose sanctions, such as imposing resolution authority, conservatorship or receivership, on such non-complying banks even when these banks continue to be solvent, thereby possibly resulting in the elimination of stockholders’ equity. Unless a bank holding company has subsidiaries other than banks that generate substantial revenues, the holding company’s cash flow and ability to declare dividends may be impaired severely by restrictions on the ability of its bank subsidiaries to declare dividends or ultimately to redeem its securities (as they mature). Similarly, U.S. and foreign laws and regulations require insurance companies to maintain minimum levels of capital and liquidity. An insurance company’s failure to maintain these capital ratios may also trigger dividend restrictions, suspensions on payments of subordinated debt, and limitations on growth. Insurance regulators (at the state-level in the United States) have broad authority in these instances and can ultimately impose sanctions, including conservatorship or receivership, on such non-complying insurance companies even when these companies continue to be solvent, thereby possibly resulting in the elimination of shareholders’ equity. In addition, insurance regulators have extensive authority in some categories of insurance of approving premium levels and setting required levels of underwriting. Companies engaged in stock brokerage, commodity brokerage, investment banking, investment management or related investment advisory services are closely tied economically to the securities and commodities markets and can suffer during a decline in either market. These companies also are subject to the regulatory environment and changes in regulations, pricing pressure, the availability of funds to borrow and interest rates. |  |  |  |  |  |  |  |  |  |  |
Market Events Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Market Events Risk. Market disruption can be caused by economic, financial or political events and factors, including but not limited to, international wars or conflicts (including Russia’s military invasion of Ukraine), geopolitical developments (including trading and tariff arrangements, sanctions and cybersecurity attacks), instability in regions such as Asia, Eastern Europe and the Middle East, terrorism, natural disasters and public health epidemics (including the outbreak of COVID-19 globally). The extent and duration of such events and resulting market disruptions cannot be predicted, but could be substantial and could magnify the impact of other risks to the Fund. These and other similar events could adversely affect the U.S. and foreign financial markets and lead to increased market volatility, reduced liquidity in the securities markets, significant negative impacts on issuers and the markets for certain securities and commodities and/or government intervention. They may also cause short- or long-term economic uncertainties in the United States and worldwide. As a result, whether or not the Fund invests in securities of issuers located in or with significant exposure to the countries directly affected, the value and liquidity of the Fund’s investments may be negatively impacted. |  |  |  |  |  |  |  |  |  |  |
Preferred Contingent Capital and Other Subordinated Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Preferred, Contingent Capital and Other Subordinated Securities Risk. Preferred, contingent capital and other subordinated securities rank lower than bonds and other debt instruments in a company’s capital structure and therefore are subject to greater credit risk than those debt instruments. Distributions on some types of these securities may also be skipped or deferred by issuers without causing a default. Finally, some of these securities typically have special redemption rights that allow the issuer to redeem the security at par earlier than scheduled. If this occurs, the Fund may be forced to reinvest in lower yielding securities. |  |  |  |  |  |  |  |  |  |  |
Contingent Capital Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Contingent Capital Securities Risk. Contingent capital securities or “CoCos” have features and risks similar to preferred and other income producing securities but also include “loss absorption” or mandatory conversion provisions and restrictions on dividend or interest payments that make the securities more like equity. This is particularly true in the financial sector, the largest preferred issuer segment. In one version of a CoCo, the security has loss absorption characteristics whereby the liquidation value of the security may be adjusted downward to below the original par value (even to zero) under certain circumstances. This may occur, for instance, in the event that business losses have eroded capital to a substantial extent. The write down of the par value would occur automatically and would not entitle the holders to seek bankruptcy of the company. In addition, an automatic write-down could result in a reduced income rate if the dividend or interest payment is based on the security’s par value. Such securities may, but are not required to, provide for circumstances under which the liquidation value may be adjusted back up to par, such as an improvement in capitalization and/or earnings. Another version of a CoCo provides for mandatory conversion of the security into common shares of the issuer under certain circumstances. The mandatory conversion might relate, for instance, to maintenance of a capital minimum, whereby falling below the minimum would trigger automatic conversion. Since the common stock of the issuer may not pay a dividend, investors in these instruments could experience a reduced income rate, potentially to zero, and conversion would deepen the subordination of the investor, hence worsening the Fund’s standing in a bankruptcy. In addition, some such instruments also provide for an automatic write-down if the price of the common stock is below the conversion price on the conversion date. An automatic write-down or conversion event is typically triggered by a reduction in the capital level of the issuer, but may also be triggered by regulatory actions (e.g., a change in capital requirements) or by other factors. In addition, interest or dividend payments may be reduced or eliminated if certain earnings or capital levels are breached. |  |  |  |  |  |  |  |  |  |  |
Credit Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Credit Risk. Credit risk is the risk that an issuer of a security will be unable or unwilling to make dividend, interest and principal payments when due and the related risk that the value of a security may decline because of concerns about the issuer’s ability to make such payments. Credit risk may be heightened for the Fund because the Fund may invest in “high yield” or “high risk” securities; such securities, while generally offering higher yields than investment grade securities with similar maturities, involve greater risks, including the possibility of default or bankruptcy, and are regarded as predominantly speculative with respect to the issuer’s capacity to pay dividends and interest and repay principal. |  |  |  |  |  |  |  |  |  |  |
High Yield Securities Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | High Yield Securities Risk. Although high yield securities generally pay higher rates of interest than investment grade securities, high yield securities are high-risk investments that may cause income and principal losses for the Fund. High yield securities may be issued by less creditworthy issuers. Issuers of high yield securities may have a larger amount of outstanding debt relative to their assets than issuers of investment grade securities. In the event of an issuer’s bankruptcy, claims of other creditors may have priority over the claims of high yield bond holders, for example, leaving few or no assets available to repay high yield bond holders. Prices of high yield securities are subject to extreme price fluctuations. Adverse changes in an issuer’s industry and general economic conditions may have a greater impact on the prices of high yield securities than on other higher rated fixed-income securities. Issuers of high yield securities may be unable to meet their interest or principal payment obligations because of an economic downturn, specific issuer developments, or the unavailability of additional financing. High yield securities frequently have redemption features that permit an issuer to repurchase the security from the Fund before it matures. If the issuer redeems high yield securities, the Fund may have to invest the proceeds in securities with lower yields and may lose income. High yield securities may be less liquid than higher rated fixed-income securities, even under normal economic conditions. There may be significant differences in the prices quoted for high yield securities by dealers in the market. Because they are less liquid, judgment may play a greater role in valuing certain of the Fund’s securities than is the case with securities trading in a more liquid market. The Fund may incur expenses to the extent necessary to seek recovery upon default or to negotiate new terms with a defaulting issuer. The credit rating of a high yield security does not necessarily address its market value risk. Ratings and market value may change from time to time, positively or negatively, to reflect new developments regarding the issuer. |  |  |  |  |  |  |  |  |  |  |
Credit Agency Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Credit Agency Risk. Credit ratings are determined by credit rating agencies and are the opinions of such entities. A rating assigned by a rating agency is not an absolute standard of credit quality and does not evaluate a security’s market risk or liquidity. Any shortcomings or inefficiencies in credit rating agencies’ processes for determining credit ratings may adversely affect the credit ratings of securities held by the Fund and, as a result, may adversely affect those securities’ perceived or actual credit risk. |  |  |  |  |  |  |  |  |  |  |
Interest Rate and Duration Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Interest Rate and Duration Risk. Interest rate risk is the risk that securities will decline in value because of changes in market interest rates. For fixed rate securities, when market interest rates rise, the market value of such securities generally will fall. Investments in fixed rate securities with long-term maturities may experience significant price declines if long-term interest rates increase. During periods of rising interest rates, the average life of certain types of securities may be extended because of slower than expected redemptions or prepayments. This may lock in a below- market yield, increase the security’s sensitivity to changes in interest rates (“duration”) and further reduce the value of the security. Fixed rate securities with longer durations tend to be more volatile than securities with shorter durations. The duration of a security will be expected to change over time with changes in market factors and time to maturity. The market value of floating-rate and fixed-to-floating rate 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 interest rate reset. A secondary risk associated with declining interest rates is the risk that income earned by the Fund on floating-rate and fixed-to-floating rate securities may decline due to lower coupon payments on floating-rate securities. |  |  |  |  |  |  |  |  |  |  |
Liquidity Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Liquidity Risk. The Fund may invest, without limit, in illiquid securities. From time to time, certain securities held by the Fund may have limited marketability and may be difficult to sell at favorable times or prices. It is possible that certain securities held by the Fund will not be able to be sold in sufficient amounts or in a sufficiently timely manner to raise the cash necessary to meet the Fund’s obligations, including potential repayment of leverage borrowings, if any. |  |  |  |  |  |  |  |  |  |  |
Foreign Investment Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Foreign Investment Risk. Because the Fund may invest its assets in foreign instruments, the value of Fund shares can be adversely affected by political and economic developments abroad. Foreign markets may be smaller, less liquid and more volatile than the major markets in the United States, and as a result, Fund share values may be more volatile. Trading in foreign markets typically involves higher expense than trading in the United States. The Fund may have difficulties enforcing its legal or contractual rights in a foreign country. Foreign legal systems generally have fewer regulatory requirements than the U.S. legal system, particularly those of emerging markets. In general, less information is publicly available with respect to non-U.S. companies than U.S. companies. Non-U.S. companies generally are not subject to the same accounting, auditing, and financial reporting standards as are U.S. companies. |  |  |  |  |  |  |  |  |  |  |
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 the Fund invests proceeds from matured, traded or redeemed securities at market interest rates that are below the Fund portfolio’s current earnings rate. For example, during periods of declining interest rates, the issuer of a security may exercise its option to redeem a security, causing the Fund to reinvest the proceeds into lower-yielding securities, which may result in a decline in the Fund’s income and distributions to Common Shareholders. |  |  |  |  |  |  |  |  |  |  |
Selection Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Selection Risk. Selection risk is the risk that the securities selected by Fund management will under-perform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. |  |  |  |  |  |  |  |  |  |  |
Management Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Management Risk. The Fund is an actively managed portfolio and its success depends upon the investment skills and analytical abilities of the Adviser to develop and effectively implement strategies that achieve the Fund’s investment objective. Decisions made by the Adviser may cause the Fund to incur losses or to miss profit opportunities. |  |  |  |  |  |  |  |  |  |  |
Leverage Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Leverage Risk. Leverage is a speculative technique and there are special risks and costs associated with leveraging. There is no assurance that leveraging strategy will be successful. Leverage involves risks and special considerations for holders of Common Shares, including: the likelihood of greater volatility of net asset value, market price and dividend rate of the Common Shares than a comparable portfolio without leverage; the risk that fluctuations in the interest or dividend rates that the Fund must pay on any leverage will reduce the return on the holders of the Common Shares; the effect of leverage in a declining market, which is likely to cause a greater decline in the net asset value of the Common Shares than if the Fund were not leveraged, which may result in a greater decline in the market price of the Common Shares; when the Fund uses financial leverage, the management fees payable to the Adviser will be higher than if the Fund did not use leverage; and leverage may increase operating costs, which may reduce total return. |  |  |  |  |  |  |  |  |  |  |
Risk of Market Price Discount from Net Asset Value [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Risk of Market Price Discount from Net Asset Value. Shares of closed-end funds frequently trade at a discount from their net asset value. This characteristic is a risk separate and distinct from the risk that net asset value could decrease as a result of investment activities. We cannot predict whether the Common Shares will trade at, above or below net asset value. |  |  |  |  |  |  |  |  |  |  |
Valuation Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Valuation Risk. Unlike publicly traded common stock that trades on national exchanges, there is no central place or exchange for trading some of the preferred and other income securities owned by the Fund. Preferred, contingent capital and debt securities generally trade on an OTC market which may be anywhere in the world where the buyer and seller can settle on a price. Due to the lack of centralized information and trading, the valuation of these securities may carry more risk than that of common stock. Uncertainties in the conditions of the financial market, unreliable reference data, lack of transparency and inconsistency of valuation models and processes may lead to inaccurate asset pricing. |  |  |  |  |  |  |  |  |  |  |
Reference Rate Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Reference Rate Risk. The Fund may be exposed to debt securities, derivatives or other financial instruments that recently transitioned from the London Interbank Offered Rate, or “LIBOR,” as a “benchmark” or “reference rate” for various interest rate calculations. LIBOR’s administrator, ICE Benchmark Administration, ceased publishing most LIBOR settings (including some U.S. LIBOR settings) by the end of 2021 and the remaining (and most widely used) U.S. Dollar LIBOR settings after June 30, 2023. The United Kingdom Financial Conduct Authority, which regulates LIBOR, will permit the use of synthetic U.S. dollar LIBOR rates for non-U.S. contracts through September 30, 2024, but any such rates would be considered non-representative of the underlying market. Since 2018 the Federal Reserve Bank of New York has published the Secured Overnight Financing Rate (referred to as SOFR), which is intended to replace U.S. Dollar LIBOR. SOFR is a broad measure of the cost of borrowing cash overnight collateralized by U.S. Treasury securities in the repurchase agreement (repo) market. There is no assurance that the composition or characteristics of SOFR or any such alternative reference rate will be similar to or produce the same value or economic equivalence as LIBOR or that the market for SOFR-linked financial instruments will have the same volume or liquidity as did the market for LIBOR-linked financial instruments prior to LIBOR’s discontinuance or unavailability. Neither the long-term effect of the LIBOR transition process nor its ultimate success can yet be known. |  |  |  |  |  |  |  |  |  |  |
Cybersecurity Risk [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Risk [Text Block] |  |  |  | Cybersecurity Risk. Cybersecurity incidents, both intentional and unintentional, may allow an unauthorized party to gain access to Fund assets, Fund or customer data (including private shareholder information), or proprietary information, cause the Fund, the Adviser, and/or their service providers (including, but not limited to, fund accountants, custodians, sub-custodians, transfer agents and financial intermediaries) to suffer data breaches, data corruption or loss of operational functionality or prevent fund investors from purchasing, redeeming or exchanging shares or receiving distributions. The Fund and the Adviser have limited ability to prevent or mitigate cybersecurity incidents affecting third party service providers, and such third-party service providers may have limited indemnification obligations to the Fund or the Adviser. Cybersecurity incidents may result in financial losses to the Fund and its shareholders, and substantial costs may be incurred in order to prevent any future cybersecurity incidents. Issuers of securities in which the Fund invests are also subject to cybersecurity risks, and the value of these securities could decline if the issuers experience cybersecurity incidents. |  |  |  |  |  |  |  |  |  |  |
Debt Outstanding [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Financial Highlights [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Securities Amount | [1] | $ 80,600 | [2] | $ 80,600 | [2] |  |  |  |  |  | $ 80,600 | $ 80,600 | $ 74,700 | $ 74,700 | $ 74,700
Senior Securities Coverage per Unit | [3] | $ 2,405 | [2] | $ 2,405 | [2] |  |  |  |  |  | $ 2,525 | $ 2,944 | $ 3,037 | $ 3,008 | $ 2,770
Common Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Description of Registrant [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Share Price |  | 7.63 |  | 7.63 |  | $ 8.06 | $ 8.25 | $ 9.14 | $ 9.58 | $ 8.60 |  |  |  |  |
NAV Per Share |  | $ 8.66 |  | $ 8.66 |  | $ 8.85 | $ 8.75 | $ 9.80 | $ 10.03 | $ 9.22 |  |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital Stock [Table Text Block] |  |  |  | 5.Common Stock At May 31, 2023, 240,000,000 shares of $0.01 par value Common Stock were authorized. The Fund has an effective “shelf” registration statement that allows it to issue shares of Common Stock periodically pursuant to Rule 415 under the Securities Act of 1933 (the “Shelf Registration Statement”). The Shelf Registration Statement permits the Fund to offer and sell Common Stock having an aggregate offering value of up to $50,000,000. Under the 1940 Act, the Fund generally may not sell Common Stock at a price below the current net asset value of such Common Stock, net of any distributing commission or discount. Accordingly, the Fund may be unable to issue Common Stock from time to time, particularly when the shares of Common Stock are trading at a discount to their net asset value. The Fund is not required to issue Common Stock pursuant to the Shelf Registration Statement and may choose not to do so. The Fund has entered into an at-the-market sales agreement (the “Sales Agreement”) with Virtu Americas LLC (“Virtu”) under which Virtu acts as the Fund’s agent or principal for the offer and sale of the Common Stock. Virtu is entitled to compensation at a commission rate of up to 1.0% of the gross sales price per share sold under the Sales Agreement. The aggregate dollar amount of Common Stock available under the Shelf Registration Statement as of May 31, 2023 was $46,762,066. Common Stock transactions were as follows:
​ | ​ | Six Months Ended 5/31/2023 | ​ | Year Ended 11/30/2022 | ​
|  | Shares |  | Amount |  | Shares |  | Amount | ​
Shares issued under the Dividend Reinvestment and Cash Purchase Plan | ​ | — | ​ | $—​ | ​ | 33,064 | ​ | $381,059​ | ​
Shares Sold through and net proceeds from Shelf Offering | ​ | — | ​ | $—​ | ​ | 40,404 | ​ | $496,118​ | ​
Costs incurred by the Fund in connection with the Shelf Registration Statement are recorded as a prepaid expense and included in “Prepaid Expenses” on the Statement of Assets and Liabilities. These costs are amortized pro rata as Common Stock is sold and are recognized and presented net as a component of “Increase from shares issued under the at-the-market program” on the Statements of Changes in Net Assets Available to Common Stock. Any deferred offering costs remaining three years after effective date of the Shelf Registration will be expensed. Costs incurred by the Fund to keep the Shelf Registration current are expensed as incurred and recognized as a component of “Expenses: Other” on the Statement of Operations. |  |  |  |  |  |  |  |  |  |  |
Outstanding Security, Authorized [Shares] |  | 240,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Outstanding Security, Held [Shares] |  | 13,077,326 |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred Shares [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital Stock, Long-Term Debt, and Other Securities [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital Stock [Table Text Block] |  |  |  | 6.Preferred Stock The Fund’s Articles of Incorporation authorize the issuance of up to 10,000,000 shares of $0.01 par value preferred stock. The Fund does not currently have any issued and outstanding shares of preferred stock. |  |  |  |  |  |  |  |  |  |  |
Outstanding Security, Authorized [Shares] |  | 10,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
[1] | See Note 7.
[2] | Unaudited
[3] | Calculated by subtracting the Fund’s total liabilities (excluding the loan) from the Fund’s total assets and dividing that amount by the loan outstanding in 000’s.

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