N-2	Nov. 30, 2022 $ / shares shares
Cover [Abstract]
Entity Central Index Key	0001282850
Amendment Flag	false
Entity Inv Company Type	N-2
Document Type	N-CSRS
Entity Registrant Name	First Trust Senior Floating Rate Income Fund II
General Description of Registrant [Abstract]
Risk Factors [Table Text Block]	Principal Risks The Fund is a 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 objectives. The following discussion summarizes the principal risks associated with investing in the Fund, which includes the risk that you could lose some or all of your investment in the Fund. The Fund is subject to the informational requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940 and, in accordance therewith, files reports, proxy statements and other information that is available for review. The order of the below risk factors does not indicate the significance of any particular risk factor. Credit Agency Risk. Credit ratings are determined by credit rating agencies and are only the opinions of such entities. Ratings assigned by a rating agency are not absolute standards of credit quality and do not evaluate market risk or the liquidity of securities. 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 or such credit rating agency’s ability to evaluate creditworthiness and, as a result, may adversely affect those securities’ perceived or actual credit risk. Credit and Below-Investment Grade Securities Risk. Credit risk is the risk that the issuer or other obligated party of a debt security in the Fund’s portfolio will fail to pay, or it is perceived that it will fail to pay, dividends or interest and/or repay principal, when due. Below-investment grade instruments, including instruments that are not rated but judged to be of comparable quality, are commonly referred to as high-yield securities or “junk” bonds and are considered speculative with respect to the issuer’s capacity to pay dividends or interest and repay principal and are more susceptible to default or decline in market value than investment grade securities due to adverse economic and business developments. High-yield securities are often unsecured and subordinated to other creditors of the issuer. The market values for high-yield securities tend to be very volatile, and these securities are generally less liquid than investment grade securities. For these reasons, an investment in the Fund is subject to the following specific risks: (i) increased price sensitivity to changing interest rates and to a deteriorating economic environment; (ii) greater risk of loss due to default or declining credit quality; (iii) adverse company specific events more likely to render the issuer unable to make dividend, interest and/or principal payments; (iv) negative perception of the high-yield market which may depress the price and liquidity of high-yield securities; (v) volatility; and (vi) liquidity. Cyber Security Risk. The Fund is susceptible to potential operational risks through breaches in cyber security. A breach in cyber security refers to both intentional and unintentional events that may cause the Fund to lose proprietary information, suffer data corruption or lose operational capacity. Such events could cause the Fund to incur regulatory penalties, reputational damage, additional compliance costs associated with corrective measures and/or financial loss. Cyber security breaches may involve unauthorized access to the Fund’s digital information systems through “hacking” or malicious software coding, but may also result from outside attacks such as denial-of-service attacks through efforts to make network services unavailable to intended users. In addition, cyber security breaches of the Fund’s third-party service providers, such as its administrator, transfer agent or custodian, or issuers in which the Fund invests, can also subject the Fund to many of the same risks associated with direct cyber security breaches. The Fund has established risk management systems designed to reduce the risks associated with cyber security. However, there is no guarantee that such efforts will succeed, especially because the Fund does not directly control the cyber security systems of issuers or third party service providers. Substantial costs may be incurred by the Fund in order to resolve or prevent cyber incidents in the future. Health Care Companies Risk. Through the Fund’s investments in senior loans, the Fund may be significantly exposed to companies in the health care sector. Health care companies are involved in medical services or health care, including biotechnology research and production, drugs and pharmaceuticals and health care facilities and services. These companies are subject to extensive competition, generic drug sales or the loss of patent protection, product liability litigation and increased government regulation. Research and development costs of bringing new drugs to market are substantial, and there is no guarantee that the product will ever come to market. Health care facility operators may be affected by the demand for services, efforts by government or insurers to limit rates, restriction of government financial assistance and competition from other providers. Illiquid Securities Risk. The Fund invests a substantial portion of its assets in lower-quality debt issued by companies that are highly leveraged. Lower-quality debt tends to be less liquid than higher-quality debt. Moreover, smaller debt issues tend to be less liquid than larger debt issues. Although the resale or secondary market for senior loans is growing, it is currently limited. There is no organized exchange or board of trade on which senior loans are traded. Instead, the secondary market for senior loans is an unregulated inter-dealer or inter-bank resale market. In addition, senior loans in which the Fund invests may require the consent of the borrower and/or agent prior to the settlement of the sale or assignment. These consent requirements can delay or impede the Fund’s ability to settle the sale of senior loans. Depending on market conditions, the Fund may have difficulty disposing its senior loans, which may adversely impact its ability to obtain cash to repay debt, to pay dividends, to pay expenses or to take advantage of new investment opportunities. Information Technology Companies Risk. Information technology companies produce and provide hardware, software and information technology systems and services. Information technology companies are generally subject to the following risks: rapidly changing technologies and existing product obsolescence; short product life cycles; fierce competition; aggressive pricing and reduced profit margins; the loss of patent, copyright and trademark protections; cyclical market patterns; evolving industry standards; and frequent new product introductions and new market entrants. Information technology companies may be smaller and less experienced companies, with limited product lines, markets or financial resources and fewer experienced management or marketing personnel. Information technology company stocks, particularly those involved with the internet, have experienced extreme price and volume fluctuations that are often unrelated to their operating performance. In addition, information technology companies are particularly vulnerable to federal, state and local government regulation, and competition and consolidation, both domestically and internationally, including competition from foreign competitors with lower production costs. Information technology companies also face competition for services of qualified personnel and heavily rely on patents and intellectual property rights and the ability to enforce such rights to maintain a competitive advantage. Interest Rate Risk. The yield on the Fund’s common shares will tend to rise or fall as market interest rates rise and fall, as senior loans pay interest at rates which float in response to changes in market rates. Changes in prevailing interest rates can be expected to cause some fluctuation in the Fund’s net asset value. Similarly, a sudden and significant increase in market interest rates may cause a decline in the Fund’s net asset value. Many financial instruments use or may use a floating rate based upon the London Interbank Offered Rate (“LIBOR”). The United Kingdom’s Financial Conduct Authority (the “FCA”), which regulates LIBOR, intends to cease making LIBOR available as a reference rate over a phase-out period that began in early 2022. However, subsequent announcements by the FCA, the LIBOR administrators, and other regulators indicate that it is possible that the most widely used LIBOR rates may continue until mid-2023. While some instruments tied to LIBOR may include a replacement rate, not all instruments have such fallback provisions and the effectiveness of such replacement rates remains uncertain. The unavailability or replacement of LIBOR may affect the value, liquidity or return on certain Fund investments and may result in costs incurred in connection with closing out positions and entering into new trades. In the United States, it is anticipated that in many instances the Secured Overnight Financing Rate (“SOFR”) will replace LIBOR as the reference rate for many of the floating rate instruments held by the Fund. There is no assurance that the composition or characteristics of SOFR, or any alternative reference rate, will be similar to or produce the same value or economic equivalence as LIBOR or that instruments using an alternative rate will have the same volume or liquidity. As a result, the transition process might lead to increased volatility and reduced liquidity in markets that currently rely on LIBOR to determine interest rates; a reduction in the value of some LIBOR-based investments; increased difficulty in borrowing or refinancing and diminished effectiveness of any applicable hedging strategies against instruments whose terms currently include LIBOR; and/ or costs incurred in connection with temporary borrowings and closing out positions and entering into new agreements. Any potential effects of the transition away from LIBOR on the Fund or on certain instruments in which the Fund invests can be difficult to ascertain, and they may vary depending on a variety of factors. Any such effects on the transition away from LIBOR, as well as other unforeseen effects, could result in losses to the Fund. Leverage Risk. The use of leverage by the Fund can magnify the effect of any losses. If the income and gains from the securities and investments purchased with leverage proceeds do not cover the cost of leverage, the return to the common shares will be less than if leverage had not been used. Leverage involves risks and special considerations for common shareholders including: (i) the likelihood of greater volatility of net asset value and market price of the common shares than a comparable portfolio without leverage; (ii) the risk that fluctuations in interest rates on borrowings will reduce the return to the common shareholders or will result in fluctuations in the dividends paid on the common shares; (iii) in a declining market, the use of leverage 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; and (iv) when the Fund uses certain types of leverage, the investment advisory fee payable to the Advisor will be higher than if the Fund did not use leverage. Management Risk and Reliance on Key Personnel. The implementation of the Fund’s investment strategy depends upon the continued contributions of certain key employees of the Advisor, some of whom have unique talents and experience and would be difficult to replace. The loss or interruption of the services of a key member of the portfolio management team could have a negative impact on the Fund. Market Discount from Net Asset Value. Shares of closed-end investment companies such as the Fund frequently trade at a discount from their net asset value. The Fund cannot predict whether its common shares will trade at, below or above net asset value. Market Risk. Securities held by a fund, as well as shares of a fund itself, are subject to market fluctuations caused by factors such as general economic conditions, political events, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Shares of a fund could decline in value or underperform other investments as a result of the risk of loss associated with these market fluctuations. In addition, local, regional or global events such as war, acts of terrorism, spread of infectious diseases or other public health issues, recessions, or other events could have a significant negative impact on a fund and its investments. For example, the coronavirus (COVID-19) global pandemic and the aggressive responses taken by many governments, including closing borders, restricting international and domestic travel, and the imposition of prolonged quarantines or similar restrictions, had negative impacts, and in many cases severe impacts, on markets worldwide. While the development of vaccines has slowed the spread of the virus and allowed for the resumption of reasonably normal business activity in the United States, many countries continue to impose lockdown measures in an attempt to slow the spread. Also, in February 2022, Russia invaded Ukraine which has caused and could continue to cause significant market disruptions and volatility across markets globally, including the United States. The hostilities and sanctions resulting from those hostilities could have a significant impact on certain Fund investments as well as Fund performance. As the global pandemic and conflict in Ukraine have illustrated, such events may affect certain geographic regions, countries, sectors and industries more significantly than others. These events also may adversely affect the prices and liquidity of the Fund’s portfolio securities or other instruments and could result in disruptions in the trading markets. Any of such circumstances could have a materially negative impact on the value of the Fund’s shares and result in increased market volatility. During any such events, the Fund’s shares may trade at increased premiums or discounts to their net asset value and the bid/ask spread on the Fund’s shares may widen. Operational Risk. The Fund is subject to risks arising from various operational factors, including, but not limited to, human error, processing and communication errors, errors of the Fund’s service providers, counterparties or other third-parties, failed or inadequate processes and technology or systems failures. The Fund relies on third parties for a range of services, including custody. Any delay or failure relating to engaging or maintaining such service providers may affect the Fund’s ability to meet its investment objectives. Although the Fund and the Advisor seek to reduce these operational risks through controls and procedures, there is no way to completely protect against such risks. Potential Conflicts of Interest Risk. First Trust and the portfolio managers have interests which may conflict with the interests of the Fund. In particular, First Trust currently manages and may in the future manage and/or advise other investment funds or accounts with the same or substantially similar investment objectives and strategies as the Fund. In addition, while the Fund is using leverage, the amount of the fees paid to First Trust for investment advisory and management services are higher than if the Fund did not use leverage because the fees paid are calculated based on managed assets. Therefore, First Trust has a financial incentive to leverage the Fund. Prepayment Risk. Loans are subject to prepayment risk. Prepayment risk is the risk that the borrower on a loan will repay principal (in part or in whole) prior to the scheduled maturity date. The degree to which borrowers prepay loans, whether as a contractual requirement or at their election, may be affected by general business conditions, interest rates, the financial condition of the borrower and competitive conditions among loan investors, among others. As such, prepayments cannot be predicted with accuracy. Upon a prepayment, either in part or in full, the actual outstanding debt on which the Fund derives interest income will be reduced. The Fund may not be able to reinvest the proceeds received on terms as favorable as the prepaid loan. Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if the Fund invests the proceeds from matured, traded or called instruments at market interest rates that are below the Fund’s portfolio’s current earnings rate. A decline in income could affect the common shares’ market price, level of distributions or the overall return of the Fund. Risks Associated with Investments in Distressed Issuers. The Fund may invest in instruments of distressed issuers, including firms that have defaulted on their debt obligations and/or filed for bankruptcy protection. Investing in such investments involves a far greater level of risk than investing in issuers whose debt obligations are being met and whose debt trades at or close to its “par” value. These investments are highly speculative with respect to the issuer’s ability to continue to make interest payments and/or to pay its principal obligations in full; can be very difficult to properly value, making them susceptible to a high degree of price volatility and rendering them less liquid than performing debt obligations; and, for issuers involved in a bankruptcy proceeding, can be subject to a high degree of uncertainty with regard to both the timing and the amount of the ultimate settlement. Second Lien Loan Risk. A second lien loan may have a claim on the same collateral pool as the first lien or it may be secured by a separate set of assets. Second lien loans are typically secured by a second priority security interest or lien on specified collateral securing the borrower’s obligation under the interest. Because second lien loans are second to first lien loans, they present a greater degree of investment risk. Specifically, these loans are subject to the additional risk that the cash flow of the borrower and property securing the loan may be insufficient to meet scheduled payments after giving effect to those loans with a higher priority. In addition, loans that have a lower than first lien priority on collateral of the borrower generally have greater price volatility than those loans with a higher priority and may be less liquid. Senior Loan Risk. The Fund invests in senior loans and therefore is subject to the risks associated therewith. Investments in senior loans are subject to the same risks as investments in other types of debt securities, including credit risk, interest rate risk, liquidity risk and valuation risk (which may be heightened because of the limited public information available regarding senior loans and because loan borrowers may be leveraged and tend to be more adversely affected by changes in market or economic conditions). Further, no active trading market may exist for certain senior loans, which may impair the ability of the Fund to realize full value in the event of the need to sell a senior loan and which may make it difficult to value senior loans. Senior loans may not be considered “securities” and the Fund may not be entitled to rely on the anti-fraud protections of the federal securities laws. In the event a borrower fails to pay scheduled interest or principal payments on a senior loan held by the Fund, the Fund will experience a reduction in its income and a decline in the value of the senior loan, which will likely reduce dividends and lead to a decline in the net asset value of the Fund’s common shares. If the Fund acquires a senior loan from another lender, for example, by acquiring a participation, the Fund may also be subject to credit risks with respect to that lender. Although senior loans may be secured by specific collateral, the value of the collateral may not equal the Fund’s investment when the senior loan is acquired or may decline below the principal amount of the senior loan subsequent to the Fund’s investment. Also, to the extent that collateral consists of stock of the borrower or its subsidiaries or affiliates, the Fund bears the risk that the stock may decline in value, be relatively illiquid, and/or may lose all or substantially all of its value, causing the senior loan to be under collateralized. Therefore, the liquidation of the collateral underlying a senior loan may not satisfy the issuer’s obligation to the Fund in the event of non-payment of scheduled interest or principal, and the collateral may not be readily liquidated. The senior loan market has seen a significant increase in loans with weaker lender protections including, but not limited to, limited financial maintenance covenants or, in some cases, no financial maintenance covenants (i.e., “covenant-lite loans”) that would typically be included in a traditional loan agreement and general weakening of other restrictive covenants applicable to the borrower such as limitations on incurrence of additional debt, restrictions on payments of junior debt or restrictions on dividends and distributions. Weaker lender protections such as the absence of financial maintenance covenants in a loan agreement and the inclusion of “borrower-favorable” terms may impact recovery values and/or trading levels of senior loans in the future. The absence of financial maintenance covenants in a loan agreement generally means that the lender may not be able to declare a default if financial performance deteriorates. This may hinder the Fund’s ability to reprice credit risk associated with a particular borrower and reduce the Fund’s ability to restructure a problematic loan and mitigate potential loss. As a result, the Fund’s exposure to losses on investments in senior loans may be increased, especially during a downturn in the credit cycle or changes in market or economic conditions. Valuation Risk. The valuation of senior loans may carry more risk than that of common stock. Because the secondary market for senior loans is limited, it may be difficult to value the loans held by the Fund. Market quotations may not be readily available for some senior loans and valuation may require more research than for liquid securities. In addition, elements of judgment may play a greater role in the valuation of senior loans than for securities with a secondary market, because there is less reliable objective data available. These difficulties may lead to inaccurate asset pricing.
Latest Share Price	$ 10.18
Latest NAV	$ 11.03
Capital Stock, Long-Term Debt, and Other Securities [Abstract]
Outstanding Security, Title [Text Block]	Common Shares
Outstanding Security, Held [Shares] \| shares	25,983,388
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 only the opinions of such entities. Ratings assigned by a rating agency are not absolute standards of credit quality and do not evaluate market risk or the liquidity of securities. 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 or such credit rating agency’s ability to evaluate creditworthiness and, as a result, may adversely affect those securities’ perceived or actual credit risk.
Credit And Below Investment Grade Securities Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Credit and Below-Investment Grade Securities Risk. Credit risk is the risk that the issuer or other obligated party of a debt security in the Fund’s portfolio will fail to pay, or it is perceived that it will fail to pay, dividends or interest and/or repay principal, when due. Below-investment grade instruments, including instruments that are not rated but judged to be of comparable quality, are commonly referred to as high-yield securities or “junk” bonds and are considered speculative with respect to the issuer’s capacity to pay dividends or interest and repay principal and are more susceptible to default or decline in market value than investment grade securities due to adverse economic and business developments. High-yield securities are often unsecured and subordinated to other creditors of the issuer. The market values for high-yield securities tend to be very volatile, and these securities are generally less liquid than investment grade securities. For these reasons, an investment in the Fund is subject to the following specific risks: (i) increased price sensitivity to changing interest rates and to a deteriorating economic environment; (ii) greater risk of loss due to default or declining credit quality; (iii) adverse company specific events more likely to render the issuer unable to make dividend, interest and/or principal payments; (iv) negative perception of the high-yield market which may depress the price and liquidity of high-yield securities; (v) volatility; and (vi) liquidity.
Cyber Security Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Cyber Security Risk. The Fund is susceptible to potential operational risks through breaches in cyber security. A breach in cyber security refers to both intentional and unintentional events that may cause the Fund to lose proprietary information, suffer data corruption or lose operational capacity. Such events could cause the Fund to incur regulatory penalties, reputational damage, additional compliance costs associated with corrective measures and/or financial loss. Cyber security breaches may involve unauthorized access to the Fund’s digital information systems through “hacking” or malicious software coding, but may also result from outside attacks such as denial-of-service attacks through efforts to make network services unavailable to intended users. In addition, cyber security breaches of the Fund’s third-party service providers, such as its administrator, transfer agent or custodian, or issuers in which the Fund invests, can also subject the Fund to many of the same risks associated with direct cyber security breaches. The Fund has established risk management systems designed to reduce the risks associated with cyber security. However, there is no guarantee that such efforts will succeed, especially because the Fund does not directly control the cyber security systems of issuers or third party service providers. Substantial costs may be incurred by the Fund in order to resolve or prevent cyber incidents in the future.
Health Care Companies Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Health Care Companies Risk. Through the Fund’s investments in senior loans, the Fund may be significantly exposed to companies in the health care sector. Health care companies are involved in medical services or health care, including biotechnology research and production, drugs and pharmaceuticals and health care facilities and services. These companies are subject to extensive competition, generic drug sales or the loss of patent protection, product liability litigation and increased government regulation. Research and development costs of bringing new drugs to market are substantial, and there is no guarantee that the product will ever come to market. Health care facility operators may be affected by the demand for services, efforts by government or insurers to limit rates, restriction of government financial assistance and competition from other providers.
Illiquid Securities Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Illiquid Securities Risk. The Fund invests a substantial portion of its assets in lower-quality debt issued by companies that are highly leveraged. Lower-quality debt tends to be less liquid than higher-quality debt. Moreover, smaller debt issues tend to be less liquid than larger debt issues. Although the resale or secondary market for senior loans is growing, it is currently limited. There is no organized exchange or board of trade on which senior loans are traded. Instead, the secondary market for senior loans is an unregulated inter-dealer or inter-bank resale market. In addition, senior loans in which the Fund invests may require the consent of the borrower and/or agent prior to the settlement of the sale or assignment. These consent requirements can delay or impede the Fund’s ability to settle the sale of senior loans. Depending on market conditions, the Fund may have difficulty disposing its senior loans, which may adversely impact its ability to obtain cash to repay debt, to pay dividends, to pay expenses or to take advantage of new investment opportunities.
Information Technology Companies Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Information Technology Companies Risk. Information technology companies produce and provide hardware, software and information technology systems and services. Information technology companies are generally subject to the following risks: rapidly changing technologies and existing product obsolescence; short product life cycles; fierce competition; aggressive pricing and reduced profit margins; the loss of patent, copyright and trademark protections; cyclical market patterns; evolving industry standards; and frequent new product introductions and new market entrants. Information technology companies may be smaller and less experienced companies, with limited product lines, markets or financial resources and fewer experienced management or marketing personnel. Information technology company stocks, particularly those involved with the internet, have experienced extreme price and volume fluctuations that are often unrelated to their operating performance. In addition, information technology companies are particularly vulnerable to federal, state and local government regulation, and competition and consolidation, both domestically and internationally, including competition from foreign competitors with lower production costs. Information technology companies also face competition for services of qualified personnel and heavily rely on patents and intellectual property rights and the ability to enforce such rights to maintain a competitive advantage.
Interest Rate Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Interest Rate Risk. The yield on the Fund’s common shares will tend to rise or fall as market interest rates rise and fall, as senior loans pay interest at rates which float in response to changes in market rates. Changes in prevailing interest rates can be expected to cause some fluctuation in the Fund’s net asset value. Similarly, a sudden and significant increase in market interest rates may cause a decline in the Fund’s net asset value. Many financial instruments use or may use a floating rate based upon the London Interbank Offered Rate (“LIBOR”). The United Kingdom’s Financial Conduct Authority (the “FCA”), which regulates LIBOR, intends to cease making LIBOR available as a reference rate over a phase-out period that began in early 2022. However, subsequent announcements by the FCA, the LIBOR administrators, and other regulators indicate that it is possible that the most widely used LIBOR rates may continue until mid-2023. While some instruments tied to LIBOR may include a replacement rate, not all instruments have such fallback provisions and the effectiveness of such replacement rates remains uncertain. The unavailability or replacement of LIBOR may affect the value, liquidity or return on certain Fund investments and may result in costs incurred in connection with closing out positions and entering into new trades. In the United States, it is anticipated that in many instances the Secured Overnight Financing Rate (“SOFR”) will replace LIBOR as the reference rate for many of the floating rate instruments held by the Fund. There is no assurance that the composition or characteristics of SOFR, or any alternative reference rate, will be similar to or produce the same value or economic equivalence as LIBOR or that instruments using an alternative rate will have the same volume or liquidity. As a result, the transition process might lead to increased volatility and reduced liquidity in markets that currently rely on LIBOR to determine interest rates; a reduction in the value of some LIBOR-based investments; increased difficulty in borrowing or refinancing and diminished effectiveness of any applicable hedging strategies against instruments whose terms currently include LIBOR; and/ or costs incurred in connection with temporary borrowings and closing out positions and entering into new agreements. Any potential effects of the transition away from LIBOR on the Fund or on certain instruments in which the Fund invests can be difficult to ascertain, and they may vary depending on a variety of factors. Any such effects on the transition away from LIBOR, as well as other unforeseen effects, could result in losses to the Fund.
Leverage Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Leverage Risk. The use of leverage by the Fund can magnify the effect of any losses. If the income and gains from the securities and investments purchased with leverage proceeds do not cover the cost of leverage, the return to the common shares will be less than if leverage had not been used. Leverage involves risks and special considerations for common shareholders including: (i) the likelihood of greater volatility of net asset value and market price of the common shares than a comparable portfolio without leverage; (ii) the risk that fluctuations in interest rates on borrowings will reduce the return to the common shareholders or will result in fluctuations in the dividends paid on the common shares; (iii) in a declining market, the use of leverage 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; and (iv) when the Fund uses certain types of leverage, the investment advisory fee payable to the Advisor will be higher than if the Fund did not use leverage.
Management Risk And Reliance On Key Personnel [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Management Risk and Reliance on Key Personnel. The implementation of the Fund’s investment strategy depends upon the continued contributions of certain key employees of the Advisor, some of whom have unique talents and experience and would be difficult to replace. The loss or interruption of the services of a key member of the portfolio management team could have a negative impact on the Fund.
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 such as the Fund frequently trade at a discount from their net asset value. The Fund cannot predict whether its common shares will trade at, below or above net asset value.
Market Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Market Risk. Securities held by a fund, as well as shares of a fund itself, are subject to market fluctuations caused by factors such as general economic conditions, political events, regulatory or market developments, changes in interest rates and perceived trends in securities prices. Shares of a fund could decline in value or underperform other investments as a result of the risk of loss associated with these market fluctuations. In addition, local, regional or global events such as war, acts of terrorism, spread of infectious diseases or other public health issues, recessions, or other events could have a significant negative impact on a fund and its investments. For example, the coronavirus (COVID-19) global pandemic and the aggressive responses taken by many governments, including closing borders, restricting international and domestic travel, and the imposition of prolonged quarantines or similar restrictions, had negative impacts, and in many cases severe impacts, on markets worldwide. While the development of vaccines has slowed the spread of the virus and allowed for the resumption of reasonably normal business activity in the United States, many countries continue to impose lockdown measures in an attempt to slow the spread. Also, in February 2022, Russia invaded Ukraine which has caused and could continue to cause significant market disruptions and volatility across markets globally, including the United States. The hostilities and sanctions resulting from those hostilities could have a significant impact on certain Fund investments as well as Fund performance. As the global pandemic and conflict in Ukraine have illustrated, such events may affect certain geographic regions, countries, sectors and industries more significantly than others. These events also may adversely affect the prices and liquidity of the Fund’s portfolio securities or other instruments and could result in disruptions in the trading markets. Any of such circumstances could have a materially negative impact on the value of the Fund’s shares and result in increased market volatility. During any such events, the Fund’s shares may trade at increased premiums or discounts to their net asset value and the bid/ask spread on the Fund’s shares may widen.
Operational Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Operational Risk. The Fund is subject to risks arising from various operational factors, including, but not limited to, human error, processing and communication errors, errors of the Fund’s service providers, counterparties or other third-parties, failed or inadequate processes and technology or systems failures. The Fund relies on third parties for a range of services, including custody. Any delay or failure relating to engaging or maintaining such service providers may affect the Fund’s ability to meet its investment objectives. Although the Fund and the Advisor seek to reduce these operational risks through controls and procedures, there is no way to completely protect against such risks.
Potential Conflicts Of Interest Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Potential Conflicts of Interest Risk. First Trust and the portfolio managers have interests which may conflict with the interests of the Fund. In particular, First Trust currently manages and may in the future manage and/or advise other investment funds or accounts with the same or substantially similar investment objectives and strategies as the Fund. In addition, while the Fund is using leverage, the amount of the fees paid to First Trust for investment advisory and management services are higher than if the Fund did not use leverage because the fees paid are calculated based on managed assets. Therefore, First Trust has a financial incentive to leverage the Fund.
Prepayment Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Prepayment Risk. Loans are subject to prepayment risk. Prepayment risk is the risk that the borrower on a loan will repay principal (in part or in whole) prior to the scheduled maturity date. The degree to which borrowers prepay loans, whether as a contractual requirement or at their election, may be affected by general business conditions, interest rates, the financial condition of the borrower and competitive conditions among loan investors, among others. As such, prepayments cannot be predicted with accuracy. Upon a prepayment, either in part or in full, the actual outstanding debt on which the Fund derives interest income will be reduced. The Fund may not be able to reinvest the proceeds received on terms as favorable as the prepaid loan.
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 the proceeds from matured, traded or called instruments at market interest rates that are below the Fund’s portfolio’s current earnings rate. A decline in income could affect the common shares’ market price, level of distributions or the overall return of the Fund.
Risks Associated With Investments In Distressed Issuers [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Risks Associated with Investments in Distressed Issuers. The Fund may invest in instruments of distressed issuers, including firms that have defaulted on their debt obligations and/or filed for bankruptcy protection. Investing in such investments involves a far greater level of risk than investing in issuers whose debt obligations are being met and whose debt trades at or close to its “par” value. These investments are highly speculative with respect to the issuer’s ability to continue to make interest payments and/or to pay its principal obligations in full; can be very difficult to properly value, making them susceptible to a high degree of price volatility and rendering them less liquid than performing debt obligations; and, for issuers involved in a bankruptcy proceeding, can be subject to a high degree of uncertainty with regard to both the timing and the amount of the ultimate settlement.
Second Lien Loan Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Second Lien Loan Risk. A second lien loan may have a claim on the same collateral pool as the first lien or it may be secured by a separate set of assets. Second lien loans are typically secured by a second priority security interest or lien on specified collateral securing the borrower’s obligation under the interest. Because second lien loans are second to first lien loans, they present a greater degree of investment risk. Specifically, these loans are subject to the additional risk that the cash flow of the borrower and property securing the loan may be insufficient to meet scheduled payments after giving effect to those loans with a higher priority. In addition, loans that have a lower than first lien priority on collateral of the borrower generally have greater price volatility than those loans with a higher priority and may be less liquid.
Senior Loan Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Senior Loan Risk. The Fund invests in senior loans and therefore is subject to the risks associated therewith. Investments in senior loans are subject to the same risks as investments in other types of debt securities, including credit risk, interest rate risk, liquidity risk and valuation risk (which may be heightened because of the limited public information available regarding senior loans and because loan borrowers may be leveraged and tend to be more adversely affected by changes in market or economic conditions). Further, no active trading market may exist for certain senior loans, which may impair the ability of the Fund to realize full value in the event of the need to sell a senior loan and which may make it difficult to value senior loans. Senior loans may not be considered “securities” and the Fund may not be entitled to rely on the anti-fraud protections of the federal securities laws. In the event a borrower fails to pay scheduled interest or principal payments on a senior loan held by the Fund, the Fund will experience a reduction in its income and a decline in the value of the senior loan, which will likely reduce dividends and lead to a decline in the net asset value of the Fund’s common shares. If the Fund acquires a senior loan from another lender, for example, by acquiring a participation, the Fund may also be subject to credit risks with respect to that lender. Although senior loans may be secured by specific collateral, the value of the collateral may not equal the Fund’s investment when the senior loan is acquired or may decline below the principal amount of the senior loan subsequent to the Fund’s investment. Also, to the extent that collateral consists of stock of the borrower or its subsidiaries or affiliates, the Fund bears the risk that the stock may decline in value, be relatively illiquid, and/or may lose all or substantially all of its value, causing the senior loan to be under collateralized. Therefore, the liquidation of the collateral underlying a senior loan may not satisfy the issuer’s obligation to the Fund in the event of non-payment of scheduled interest or principal, and the collateral may not be readily liquidated. The senior loan market has seen a significant increase in loans with weaker lender protections including, but not limited to, limited financial maintenance covenants or, in some cases, no financial maintenance covenants (i.e., “covenant-lite loans”) that would typically be included in a traditional loan agreement and general weakening of other restrictive covenants applicable to the borrower such as limitations on incurrence of additional debt, restrictions on payments of junior debt or restrictions on dividends and distributions. Weaker lender protections such as the absence of financial maintenance covenants in a loan agreement and the inclusion of “borrower-favorable” terms may impact recovery values and/or trading levels of senior loans in the future. The absence of financial maintenance covenants in a loan agreement generally means that the lender may not be able to declare a default if financial performance deteriorates. This may hinder the Fund’s ability to reprice credit risk associated with a particular borrower and reduce the Fund’s ability to restructure a problematic loan and mitigate potential loss. As a result, the Fund’s exposure to losses on investments in senior loans may be increased, especially during a downturn in the credit cycle or changes in market or economic conditions.
Valuation Risk [Member]
General Description of Registrant [Abstract]
Risk [Text Block]	Valuation Risk. The valuation of senior loans may carry more risk than that of common stock. Because the secondary market for senior loans is limited, it may be difficult to value the loans held by the Fund. Market quotations may not be readily available for some senior loans and valuation may require more research than for liquid securities. In addition, elements of judgment may play a greater role in the valuation of senior loans than for securities with a secondary market, because there is less reliable objective data available. These difficulties may lead to inaccurate asset pricing.