| N-2 - USD ($) | 3 Months Ended | 12 Months Ended | ||||||||||||||||
| Mar. 31, 2024 | Dec. 31, 2023 | Sep. 30, 2023 | Jun. 30, 2023 | Mar. 31, 2023 | Dec. 31, 2022 | Sep. 30, 2022 | Jun. 30, 2022 | Mar. 31, 2024 | Mar. 31, 2022 | Mar. 31, 2021 | Mar. 31, 2020 | Mar. 31, 2019 | Mar. 31, 2018 | Mar. 31, 2017 | Mar. 31, 2016 | Mar. 31, 2015 | ||
| Cover [Abstract] | ||||||||||||||||||
| Entity Central Index Key | 0001478888 | |||||||||||||||||
| Amendment Flag | false | |||||||||||||||||
| Document Type | N-CSR | |||||||||||||||||
| Entity Registrant Name | Nuveen Taxable Municipal Income Fund | |||||||||||||||||
| Fee Table [Abstract] | ||||||||||||||||||
| Shareholder Transaction Expenses [Table Text Block] | SUMMARY OF FUND EXPENSES The purpose of the tables and the example below are to help you understand all fees and expenses that you, as a common shareholder, would bear directly or indirectly. The tables show the expenses of the Fund as a percentage of the average net assets applicable to Common Shares and not as a percentage of total assets or managed assets. Shareholder Transaction Expenses Maximum Sales Charge (as a percentage of offering price (1) 1.00% Dividend Reinvestment Plan Fees (2) $2.50 (1) The maximum sales charge for offerings made at-the-market at-the-market, (2) You will be charged a $2.50 service charge and pay brokerage charges if you direct Computershare Inc. and Computershare Trust Company, N.A., as agent for the common shareholders, to sell your Common Shares held in a dividend reinvestment account. | |||||||||||||||||
| Sales Load [Percent] | [1] | 1% | ||||||||||||||||
| Dividend Reinvestment and Cash Purchase Fees | [2] | $ 2.5 | ||||||||||||||||
| Other Transaction Expenses [Abstract] | ||||||||||||||||||
| Annual Expenses [Table Text Block] | Annual Expenses (As a Percentage of Net Assets Attributable to Common Shares) (1) Management Fees 0.98% Interest and Other Related Expenses (2) 2.58% Other Expenses (3) 0.07% Total Annual Expenses 3.63% (1) Stated as percentages of average net assets attributable to Common Shares for the fiscal year ended March 31, 2024. (2) Interest and Other Related Expenses reflect actual expenses and fees for leverage incurred by the Fund for the fiscal year ended March 31, 2024. The types of leverage used by the Fund during the fiscal year ended March 31, 2024 are described in the Fund Leverage and the Notes to Financial Statements sections of this annual report. Actual Interest and Other Related Expenses incurred in the future may be higher or lower. If short-term market interest rates rise in the future, and if the Fund continues to maintain leverage, the cost of which is tied to short-term interest rates, the Fund’s interest expenses on its short-term borrowings can be expected to rise in tandem. The Fund’s use of leverage will increase the amount of management fees paid to the Fund’s adviser and sub-advisor(s). (3) Other Expenses are based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%. | |||||||||||||||||
| Management Fees [Percent] | [3] | 0.98% | ||||||||||||||||
| Interest Expenses on Borrowings [Percent] | [3],[4] | 2.58% | ||||||||||||||||
| Other Annual Expenses [Abstract] | ||||||||||||||||||
| Other Annual Expenses [Percent] | [3],[5] | 0.07% | ||||||||||||||||
| Total Annual Expenses [Percent] | [3] | 3.63% | ||||||||||||||||
| Expense Example [Table Text Block] | Example The following example illustrates the expenses, including the applicable transaction fees (referred to as the “Maximum Sales Charge” in the Shareholder Transaction Expenses table above), if any, that a common shareholder would pay on a $1,000 investment that is held for the time periods provided in the table. The example assumes that all dividends and other distributions are reinvested in the Fund and that the Fund’s Annual Expenses, as provided above, remain the same. The example also assumes a 5% annual return. Actual expenses may be greater or less than those assumed. Moreover, the Fund’s actual rate of return may be greater or less than the hypothetical 5% return shown in the example. Example (At-the-Market The following example assumes a transaction fee of 1.00%, as a percentage of the offering price. 1 Year 3 Years 5 Years 10 Years $46 $120 $196 $395 The example should not be considered a representation of future expenses. Actual expenses may be greater or less than those shown above. | |||||||||||||||||
| Expense Example, Year 01 | $ 46 | |||||||||||||||||
| Expense Example, Years 1 to 3 | 120 | |||||||||||||||||
| Expense Example, Years 1 to 5 | 196 | |||||||||||||||||
| Expense Example, Years 1 to 10 | $ 395 | |||||||||||||||||
| Purpose of Fee Table , Note [Text Block] | The purpose of the tables and the example below are to help you understand all fees and expenses that you, as a common shareholder, would bear directly or indirectly. The tables show the expenses of the Fund as a percentage of the average net assets applicable to Common Shares and not as a percentage of total assets or managed assets. | |||||||||||||||||
| Basis of Transaction Fees, Note [Text Block] | as a percentage of offering price | |||||||||||||||||
| Other Expenses, Note [Text Block] | Other Expenses are based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%. | |||||||||||||||||
| Financial Highlights [Abstract] | ||||||||||||||||||
| Senior Securities [Table Text Block] | The following table sets forth information regarding the Fund’s outstanding senior securities as of the end of the Fund’s last ten fiscal periods, as applicable. The Fund’s senior securities during this time period are comprised of borrowings that constitute “senior securities” as defined in the Investment Company Act of 1940, as amended (1940 Act). The information in this table as of and for the fiscal years ended 2024 through 2015 has been audited by KPMG LLP, independent registered public accounting firm. The information with respect to the fiscal years ended prior to 2015, where applicable, has been audited by other auditors. The Funds’ audited financial statements, including the report of KPMG LLP thereon, and accompanying notes thereto, are included in this Annual Report. Borrowings Outstanding at the End of Period Year Ended 3/31: Aggregate Amount Outstanding (000) (1) Asset Coverage Per $1,000 (2) 2024 $ 0 $ 0 2023 0 0 2022 0 0 2021 0 0 2020 0 0 2019 0 0 2018 90,175 7,445 2017 90,175 7,281 2016 89,500 7,532 2015 89,500 7,839 (1) Aggregate Amount Outstanding: Aggregate amount outstanding represents the liquidation preference as of the end of the relevant fiscal year and does not include any preferred shares noticed for redemption as noted on the Statement of Assets and Liabilities where applicable. (2) Asset Coverage Per $1,000: Asset coverage per $1,000 is calculated by subtracting the Fund’s liabilities and indebtedness not represented by senior securities from the Fund’s total assets, dividing the result by the aggregate amount of the Fund’s senior securities representing indebtedness then outstanding (if applicable), plus the aggregate of the involuntary liquidation preference of the outstanding preferred shares, if applicable, and multiplying the result by 1,000. | |||||||||||||||||
| Senior Securities Amount | [6] | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 90,175,000 | $ 90,175,000 | $ 89,500,000 | $ 89,500,000 | ||||||
| Senior Securities Coverage per Unit | [7] | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 7,445 | $ 7,281 | $ 7,532 | $ 7,839 | ||||||
| Senior Securities, Note [Text Block] | SENIOR SECURITIES The following table sets forth information regarding the Fund’s outstanding senior securities as of the end of the Fund’s last ten fiscal periods, as applicable. The Fund’s senior securities during this time period are comprised of borrowings that constitute “senior securities” as defined in the Investment Company Act of 1940, as amended (1940 Act). The information in this table as of and for the fiscal years ended 2024 through 2015 has been audited by KPMG LLP, independent registered public accounting firm. The information with respect to the fiscal years ended prior to 2015, where applicable, has been audited by other auditors. The Funds’ audited financial statements, including the report of KPMG LLP thereon, and accompanying notes thereto, are included in this Annual Report. Borrowings Outstanding at the End of Period Year Ended 3/31: Aggregate Amount Outstanding (000) (1) Asset Coverage Per $1,000 (2) 2024 $ 0 $ 0 2023 0 0 2022 0 0 2021 0 0 2020 0 0 2019 0 0 2018 90,175 7,445 2017 90,175 7,281 2016 89,500 7,532 2015 89,500 7,839 (1) Aggregate Amount Outstanding: Aggregate amount outstanding represents the liquidation preference as of the end of the relevant fiscal year and does not include any preferred shares noticed for redemption as noted on the Statement of Assets and Liabilities where applicable. (2) Asset Coverage Per $1,000: Asset coverage per $1,000 is calculated by subtracting the Fund’s liabilities and indebtedness not represented by senior securities from the Fund’s total assets, dividing the result by the aggregate amount of the Fund’s senior securities representing indebtedness then outstanding (if applicable), plus the aggregate of the involuntary liquidation preference of the outstanding preferred shares, if applicable, and multiplying the result by 1,000. | |||||||||||||||||
| Senior Securities Headings, Note [Text Block] | The following table sets forth information regarding the Fund’s outstanding senior securities as of the end of the Fund’s last ten fiscal periods, as applicable. The Fund’s senior securities during this time period are comprised of borrowings that constitute “senior securities” as defined in the Investment Company Act of 1940, as amended (1940 Act). The information in this table as of and for the fiscal years ended 2024 through 2015 has been audited by KPMG LLP, independent registered public accounting firm. The information with respect to the fiscal years ended prior to 2015, where applicable, has been audited by other auditors. The Funds’ audited financial statements, including the report of KPMG LLP thereon, and accompanying notes thereto, are included in this Annual Report. | |||||||||||||||||
| Senior Securities Highlights Audited, Note [Text Block] | The information in this table as of and for the fiscal years ended 2024 through 2015 has been audited by KPMG LLP, independent registered public accounting firm. The information with respect to the fiscal years ended prior to 2015, where applicable, has been audited by other auditors. The Funds’ audited financial statements, including the report of KPMG LLP thereon, and accompanying notes thereto, are included in this Annual Report. | |||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Investment Objectives and Practices [Text Block] | Investment Objective The Fund’s primary investment objective is to provide current income through investments in taxable municipal securities. As a secondary objective, the Fund seeks to enhance portfolio value and total return. Investment Policies Under normal circumstances, the Fund will invest at least 80% of its Assets (as defined below) in taxable municipal securities. The Fund may invest up to 20% of its Assets in securities other than taxable municipal securities, including municipal securities the interest income from which is exempt from regular federal income tax (sometimes referred to as “tax-exempt “Assets” mean the net assets of the Fund plus the amount of any borrowings for investment purposes. “Managed Assets” mean the total assets of the Fund, minus the sum of its accrued liabilities (other than Fund liabilities incurred for the express purpose of creating leverage). Total assets for this purpose shall include assets attributable to the Fund’s use of leverage (whether or not those assets are reflected in the Fund’s financial statements for purposes of generally accepted accounting principles), and derivatives will be valued at their market value. Under normal circumstances: · The Fund will invest at least 80% of its Managed Assets in municipal securities that, at the time of investment, are rated within the four highest grades (Baa or BBB or better) by at least one nationally recognized statistical rating organization (an “NRSRO”) or are unrated but judged to be of comparable quality by the Fund’s sub-adviser. · The Fund may invest up to 20% of its Managed Assets in municipal securities that at the time of investment are rated below investment grade or are unrated but judged to be of comparable quality by the Fund’s sub-adviser. · The Fund will not invest more than 25% of its Managed Assets in municipal securities in any one industry or in any one state of origin. · The Fund may invest up to 20% of its total assets in certain derivative instruments to enhance returns. Such derivatives include financial futures contracts, swap contracts (including interest rate and credit default swaps), options on financial futures, options on swap contracts, or similar instruments. This limit will apply to the investment exposure created by those derivative instruments. Inverse floating rate securities are not regarded as derivatives for this purpose. The Fund’s sub-adviser · The Fund may invest up to 10% of its Managed Assets in securities of other open- or closed-end · The Fund will generally maintain an investment portfolio with an overall weighted average maturity of greater than 10 years. The foregoing policies apply only at the time of any new investment. Approving Changes in Investment Policies The Board of Trustees of the Fund may change the policies described above without a shareholder vote. However, the Fund’s investment objectives may not be changed without the approval of the holders of a majority of the outstanding common shares and preferred shares voting together as a single class, and the approval of the holders of a majority of the outstanding preferred shares, voting separately as a single class. A “majority of the outstanding” shares means (i) 67% or more of the shares present at a meeting, if the holders of more than 50% of the shares are present or represented by proxy or (ii) more than 50% of the shares, whichever is less. Additionally, with respect to the Fund’s policy of investing at least 80% of its Assets in taxable municipal securities, such policy may not be changed without 60 days’ prior notice to shareholders. Portfolio Contents The Fund generally invests in taxable municipal securities (including Build America Bonds (“BABs”)) and tax-exempt pre-refunded Municipal securities are debt obligations generally issued by states, cities and local authorities and certain possessions and territories of the United States (such as Puerto Rico and Guam) to finance or refinance public purpose projects such as roads, schools, and water supply systems. BABs are taxable municipal obligations issued pursuant to the American Recovery and Reinvestment Act of 2009 that are subject to federal subsidies of up to 35% of the interest payable on the bonds in the form of direct subsidies to the bond issuer or refundable tax credits to the bond holder. Build America Bonds are not guaranteed by the U.S. government or its agencies or instrumentalities. The Fund may invest in municipal securities that represent lease obligations and certificates of participation in such leases. A municipal lease is an obligation in the form of a lease or installment purchase that is issued by a state or local government to acquire equipment and facilities. Income from such obligations generally is exempt from state and local taxes in the state of issuance. A certificate of participation represents an undivided interest in an unmanaged pool of municipal leases, an installment purchase agreement or other instruments. The certificates typically are issued by a municipal agency, a trust or other entity that has received an assignment of the payments to be made by the state or political subdivision under such leases or installment purchase agreements. Such certificates provide the Fund with the right to a pro rata undivided interest in the underlying municipal securities. In addition, such participations generally provide the Fund with the right to demand payment, on not more than seven days’ notice, of all or any part of the Fund’s participation interest in the underlying municipal securities, plus accrued interest. The Fund may invest in municipal notes. Municipal securities in the form of notes generally are used to provide for short-term capital needs, in anticipation of an issuer’s receipt of other revenues or financing, and typically have maturities of up to three years. Such instruments may include tax anticipation notes, revenue anticipation notes, bond anticipation notes, tax and revenue anticipation notes and construction loan notes. Tax anticipation notes are issued to finance the working capital needs of governments. Generally, they are issued in anticipation of various tax revenues, such as income, sales, property, use and business taxes, and are payable from these specific future taxes. Revenue anticipation notes are issued in expectation of receipt of other kinds of revenue, such as federal revenues available under federal revenue sharing programs. Bond anticipation notes are issued to provide interim financing until long-term bond financing can be arranged. In most cases, the long-term bonds then provide the funds needed for repayment of the bond anticipation notes. Tax and revenue anticipation notes combine the funding sources of both tax anticipation notes and revenue anticipation notes. Construction loan notes are sold to provide construction financing. Mortgage notes insured by the Federal Housing Authority secure these notes; however, the proceeds from the insurance may be less than the economic equivalent of the payment of principal and interest on the mortgage note if there has been a default. The anticipated revenues from taxes, grants or bond financing generally secure the obligations of an issuer of municipal notes. The Fund may invest in pre-refunded pre-refunded pre-refunded pre-refunded pre-refunded The Fund may invest in private activity bonds. Private activity bonds are issued by or on behalf of public authorities to obtain funds to provide privately operated housing facilities, airport, mass transit or port facilities, sewage disposal, solid waste disposal or hazardous waste treatment or disposal facilities and certain local facilities for water supply, gas or electricity. Other types of private activity bonds, the proceeds of which are used for the construction, equipment, repair or improvement of privately operated industrial or commercial facilities, may constitute municipal securities, although the current federal tax laws place substantial limitations on the size of such issues. The Fund may invest in inverse floating rate securities issued by a TOB trust, the interest rate on which varies inversely with the Securities Industry Financial Markets Association short-term rate, which resets weekly, or a similar short-term rate, and is reduced by the expenses related to the TOB trust. Typically, inverse floating rate securities represent beneficial interests in a special purpose trust (sometimes called a TOB trust) formed by a third party sponsor for the purpose of holding municipal bonds. Inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate on the municipal bond held by the TOB trust, which effectively leverages the Fund’s investment. The Fund may invest in floating rate securities issued by special purpose trusts. Floating rate securities may take the form of short-term floating rate securities or the option period may be substantially longer. Generally, the interest rate earned will be based upon the market rates for municipal securities with maturities or remarketing provisions that are comparable in duration to the periodic interval of the tender option, which may vary from weekly, to monthly, to extended periods of one year or multiple years. Since the option feature has a shorter term than the final maturity or first call date of the underlying bond deposited in the trust, the Fund as the holder of the floating rate security relies upon the terms of the agreement with the financial institution furnishing the option as well as the credit strength of that institution. As further assurance of liquidity, the terms of the trust provide for a liquidation of the municipal security deposited in the trust and the application of the proceeds to pay off the floating rate security. The trusts that are organized to issue both short-term floating rate securities and inverse floaters generally include liquidation triggers to protect the investor in the floating rate security. The Fund may invest in municipal securities issued by special taxing districts. Special taxing districts are organized to plan and finance infrastructure developments to induce residential, commercial and industrial growth and redevelopment. The bond financing methods such as tax increment finance, tax assessment, special services district and Mello-Roos bonds, are generally payable solely from taxes or other revenues attributable to the specific projects financed by the bonds without recourse to the credit or taxing power of related or overlapping municipalities. The Fund may invest in zero coupon bonds. A zero coupon bond is a bond that typically does not pay interest for the entire life of the obligation or for an initial period after the issuance of the obligation. The Fund may buy and sell securities on a when-issued or delayed delivery basis, making payment or taking delivery at a later date, normally within 15 to 45 days of the trade date. The Fund may utilize structured notes and similar instruments for investment purposes and also for hedging purposes. Structured notes are privately negotiated debt obligations where the principal and/or interest is determined by reference to the performance of a benchmark asset, market or interest rate (an “embedded index”), such as selected securities, an index of securities or specified interest rates, or the differential performance of two assets or markets. The Fund may invest in illiquid securities (i.e., securities that are not readily marketable), including, but not limited to, restricted securities (securities the disposition of which is restricted under the federal securities laws), securities that may be resold only pursuant to Rule 144A under the Securities Act of 1933, as amended (the “1933 Act”), and repurchase agreements with maturities in excess of seven days. The Fund may enter into certain derivative instruments in pursuit of its investment objectives, including to seek to enhance return, to hedge certain risks of its investments in municipal securities or as a substitute for a position in the underlying asset. Such instruments include financial futures contracts, swap contracts (including interest rate swaps and credit default swaps), options on financial futures, options on swap contracts or other derivative instruments. The Fund may also invest in securities of other open- or closed-end Use of Leverage The Fund uses leverage to pursue its investment objectives. The Fund may use leverage to the extent permitted by the 1940 Act. The Fund may source leverage through a number of methods, including borrowings (including loans from financial institutions), issuances of debt securities and issuances of preferred shares of beneficial interest. The Fund may also use other forms of leverage including, but not limited to, reverse repurchase agreements and portfolio investments that have the economic effect of leverage, including, but not limited to, investments in inverse floating rate securities of TOB trusts. Integrated Leverage and Hedging Strategy The Fund employs an integrated leverage and hedging strategy to seek to enhance its potential current income and longer-term risk-adjusted total return, while seeking to maintain a level of interest rate risk comparable to that of the Bloomberg Barclays Taxable Municipal Long Bond Index (the “Index”). The Fund uses leverage instruments that will have a funding cost based on short- to intermediate-term market interest rates. Because such interest rates are expected to be generally lower than the yields on the long-term bonds in which the Fund invests, the Fund’s sub-adviser The Fund’s leverage and hedging techniques are referred to as integrated because the Fund’s use of hedging strategies is expected to be directly calibrated to any increased interest rate risk, relative to the Fund’s benchmark, due to the use of leverage. The Fund’s use of derivatives such as bond futures or interest rate swaps in hedging interest rate risk will generate costs that will effectively reduce the Fund’s net asset value (“NAV”). These capital costs may be offset over time by capital appreciation of the Fund’s portfolio. The potential to achieve such capital appreciation will depend largely on the sub-adviser’s Temporary Defensive Periods During temporary defensive periods (e.g., times when, in the Fund’s investment adviser’s and/or the Fund’s sub-adviser’s tax-exempt | |||||||||||||||||
| Risk Factors [Table Text Block] | PRINCIPAL RISKS OF THE FUND The factors that are most likely to have a material effect on the Fund’s portfolio as a whole are called “principal risks.” The Fund is subject to the principal risks indicated below, whether through direct investment or derivative positions. The Fund may be subject to additional risks other than those identified and described below because the types of investments made by the Fund can change over time. Risks of NBB Portfolio Level Risks Below Investment Grade Risk Build America Bonds (“BABs”) Risk Call Risk Credit Risk Credit Spread Risk Defaulted or Distressed Securities Risk Deflation Risk Derivatives Risk Duration Risk Economic Sector Risk Financial Futures and Options Transactions Risk Hedging Risk Illiquid Investments Risk Income Risk Inflation Risk Insurance Risk Interest Rate Risk Inverse Floating Rate Securities Risk Municipal Securities Market Liquidity Risk Municipal Securities Market Risk Other Investment Companies Risk Reinvestment Risk Special Risks Related to Certain Municipal Obligations Swap Transactions Risk Unrated Securities Risk Valuation Risk Zero Coupon Bonds Risk Fund Level and Other Risks Anti-Takeover Provisions Counterparty Risk Cybersecurity Risk Economic and Political Events Risk Fund Tax Risk Global Economic Risk Investment and Market Risk Legislation and Regulatory Risk Leverage Risk Portfolio Level Risks Market Discount from Net Asset Value Recent Market Conditions Reverse Repurchase Agreement Risk Portfolio Level Risks: Below Investment Grade Risk. Municipal securities of below investment grade quality are regarded as having speculative characteristics with respect to the issuer’s capacity to pay dividends or interest and repay principal, and may be subject to higher price volatility and default risk than investment grade municipal securities of comparable terms and duration. Issuers of lower grade municipal securities may be highly leveraged and may not have available to them more traditional methods of financing. The prices of these lower grade securities are typically more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn. The secondary market for lower rated municipal securities may not be as liquid as the secondary market for more highly rated municipal securities, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular municipal security. If a below investment grade municipal security goes into default, or its issuer enters bankruptcy, it might be difficult to sell that security in a timely manner at a reasonable price. Build America Bonds (“BABs”) Risk. BABs are taxable municipal obligations issued pursuant to the American Recovery and Reinvestment Act of 2009 that are subject to federal subsidies of up to 35% of the interest payable on the bonds in the form of direct subsidies to the bond issuer or refundable tax credits to the bond holder. BABs are not guaranteed by the U.S. government or its agencies or instrumentalities. While the federal subsidy continues for the life of the bonds, provided that the issuer continues to meet all applicable program eligibility requirements, there is no assurance that the federal subsidy will be continued at original levels. Under the sequestration process under the Budget Control Act of 2011, automatic spending cuts that became effective on March 1, 2013 reduced the federal subsidy for BABs and other subsidized taxable municipal bonds. The reduced federal subsidy has been extended through 2030. The subsidy payments were reduced by 6.6% in 2018 and 6.2% in 2019, 5.9% in 2020 and 5.7% between 2021 and 2030. Further decreases in the level of the subsidy may impair the ability of issuers to make interest payments when due. BABs were an alternative form of financing to state and local governments whose primary means for accessing the capital markets had been through issuance of tax free municipal bonds. Pursuant to the terms of the American Recovery and Reinvestment Act of 2009, the issuance of BABs ceased on December 31, 2010. As a result, the availability of such bonds is limited and there can be no assurance that BABs will be actively traded. The market for the bonds and/or their liquidity may be negatively affected. Changes to the U.S. federal income tax laws or other federal legislation may affect the demand for and supply of taxable municipal bonds, including BABs, and/or trigger extraordinary call features of the BABs. The extraordinary call features of certain BABs permit early redemption at par value, which, if triggered, could result in potential losses for the Fund if such BABs were purchased at prices above par, and may require the Fund to reinvest redemption proceeds in lower-yielding securities. BABs involve similar risks as traditional municipal bonds, including credit, call and market risk. Because certain states, including California, New York, Illinois, Texas and Ohio, were heavy issuers of BABs, the Fund may have a greater exposure to the economic or other factors affecting such states than a more diversified national municipal bond fund. In addition, should a BAB’s issuer fail to continue to meet the applicable requirements, it is possible that such issuer may not receive federal cash subsidy payments, impairing the issuer’s ability to make scheduled interest payments. BABs may be subject to greater reinvestment risk, which is the risk that the Fund is unable to invest in bonds with similar yields, as BABs with attractive above-market purchase yields mature or are called. Call Risk. Credit Risk. Issuers of municipal securities in which the Fund may invest may default on their obligations to pay principal or interest when due. This non-payment non-payment Credit Spread Risk. Defaulted or Distressed Securities Risk. Investments in “distressed” securities, meaning those whose issuers are experiencing financial difficulties or distress at the time of acquisition, present a substantial risk of future default. In the event distressed securities become defaulted securities or the Fund otherwise holds defaulted securities, the Fund may incur losses, including additional expenses, to the extent it is required to seek recovery upon a default in the payment of principal or interest on those securities. In any reorganization or liquidation proceeding relating to a portfolio security, the Fund may lose its entire investment or may be required to accept cash or securities with a value less than its original investment. Defaulted or distressed securities may be subject to restrictions on resale. Deflation Risk. Deflation risk is the risk that prices throughout the economy decline over time. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. Derivatives Risk. The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a municipal security or other asset without buying or selling the municipal security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over-the-counter It is possible that regulatory or other developments in the derivatives market, including changes in government regulation, could adversely impact the Fund’s ability to invest in certain derivatives or successfully use derivative instruments. Duration Risk. Economic Sector Risk. The Fund may invest a significant amount of its total assets in municipal securities in the same economic sector. This may make the Fund more susceptible to adverse economic, political or regulatory occurrences affecting an economic sector making the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. As the percentage of the Fund’s Managed Assets invested in a particular sector increases, so does the potential for fluctuation in the value of the Fund’s assets. In addition, the Fund may invest a significant portion of its assets in certain sectors of the municipal securities market, such as health care facilities, private educational facilities, special taxing districts and start-up Financial Futures and Options Transactions Risk. The Fund may use certain transactions for hedging the portfolio’s exposure to credit risk and the risk of increases in interest rates, which could result in poorer overall performance for the Fund. There may be an imperfect correlation between price movements of the futures and options and price movements of the portfolio securities being hedged. If the Fund engages in futures transactions or in the writing of options on futures, it will be required to maintain initial margin and maintenance margin and may be required to make daily variation margin payments in accordance with applicable rules of the exchanges and the Commodity Futures Trading Commission (“CFTC”). If the Fund purchases a financial futures contract or a call option or writes a put option in order to hedge the anticipated purchase of municipal securities, and if the Fund fails to complete the anticipated purchase transaction, the Fund may have a loss or a gain on the futures or options transaction that will not be offset by price movements in the municipal securities that were the subject of the anticipatory hedge. There can be no assurance that a liquid market will exist at a time when the Fund seeks to close out a derivatives or futures or a futures option position, and the Fund would remain obligated to meet margin requirements until the position is closed. Hedging Risk. sub-adviser’s sub-adviser’s Illiquid Investments Risk. Illiquid investments are investments that are not readily marketable. These investments may include restricted investments, including Rule 144A securities, which cannot be resold to the public without an effective registration statement under the 1933 Act, or if they are unregistered may be sold only in a privately negotiated transaction or pursuant to an available exemption from registration. The Fund may not be able to readily dispose of such investments at prices that approximate those at which the Fund could sell such investments if they were more widely traded and, as a result of such illiquidity, the Fund may have to sell other investments or engage in borrowing transactions if necessary to raise cash to meet its obligations. Limited liquidity can also affect the market price of investments, thereby adversely affecting the Fund’s NAV and ability to make dividend distributions. The financial markets in general have in recent years experienced periods of extreme secondary market supply and demand imbalance, resulting in a loss of liquidity during which market prices were suddenly and substantially below traditional measures of intrinsic value. During such periods, some investments could be sold only at arbitrary prices and with substantial losses. Periods of such market dislocation may occur again at any time. Income Risk. The Fund’s income could decline due to falling market interest rates. This is because, in a falling interest rate environment, the Fund generally will have to invest the proceeds from maturing portfolio securities in lower-yielding securities. Inflation Risk. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the common shares and distributions can decline. Currently, inflation rates are elevated relative to normal market conditions and could increase. Insurance Risk. The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub-prime Interest Rate Risk. Interest rate risk is the risk that municipal securities in the Fund’s portfolio will decline in value because of changes in market interest rates. Generally, when market interest rates rise, the market value of such securities will fall, and vice versa. As interest rates decline, issuers of municipal securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower-yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower than expected principal payments may extend the average life of municipal securities, potentially locking in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer-term municipal securities generally fluctuate more than prices of shorter-term municipal securities as interest rates change. Inverse Floating Rate Securities Risk. The Fund may invest in inverse floating rate securities. In general, income on inverse floating rate securities will decrease when short-term interest rates increase and increase when short-term interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal. In addition, inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of fixed rate securities. The Fund may invest in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities. The Fund may be required to sell its inverse floating rate securities at less than favorable prices, or liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following: · If the Fund has a need for cash and the securities in a special purpose trust are not actively trading due to adverse market conditions; · If special purpose trust sponsors (as a collective group or individually) experience financial hardship and consequently seek to terminate their respective outstanding special purpose trusts; and · If the value of an underlying security declines significantly and if additional collateral has not been posted by the Fund. Municipal Securities Market Liquidity Risk. Inventories of municipal securities held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell municipal securities at attractive prices, and increase municipal security price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of municipal securities to raise cash to meet its obligations, those sales could further reduce the municipal securities’ prices and hurt performance. Municipal Securities Market Risk. The amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the investment performance of the Fund may therefore be more dependent on the analytical abilities of the sub-adviser Other Investment Companies Risk. The Fund may invest in the securities of other investment companies, including ETFs. Investing in an investment company exposes the Fund to all of the risks of that investment company’s investments. The Fund, as a holder of the securities of other investment companies, will bear its pro rata portion of the other investment companies’ expenses, including advisory fees. These expenses are in addition to the direct expenses of the Fund’s own operations. As a result, the cost of investing in investment company shares may exceed the costs of investing directly in its underlying investments. In addition, securities of other investment companies may be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities and therefore magnify the Fund’s leverage risk. With respect to ETF’s, an ETF that is based on a specific index may not be able to replicate and maintain exactly the composition and relative weighting of securities in the index. The value of an ETF based on a specific index is subject to change as the values of its respective component assets fluctuate according to market volatility. ETFs typically rely on a limited pool of authorized participants to create and redeem shares, and an active trading market for ETF shares may not develop or be maintained. The market value of shares of ETFs and closed-end Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called municipal securities at market interest rates that are below the portfolio’s current earnings rate. A decline in income could affect the common shares’ market price, NAV and/or a common shareholder’s overall returns. Special Risks Related to Certain Municipal Obligations. Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non-appropriation” non-appropriation non-appropriation, Certificates of participation involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificates of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation. Swap Transactions Risk. The Fund may enter into debt-related derivative instruments such as credit default swap contracts and interest rate swaps. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by the investment adviser and/or the sub-adviser sub-adviser Unrated Securities Risk. Valuation Risk. The municipal securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including readily available market quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to sell a portfolio security at the price established by the pricing service, which could result in a loss to the Fund. Pricing services generally price municipal securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Different pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s NAV. Zero Coupon Bonds Risk. Because interest on zero coupon bonds is not paid on a current basis, the values of zero coupon bonds will be more volatile in response to interest rate changes than the values of bonds that distribute income regularly. Although zero coupon bonds generate income for accounting purposes, they do not produce cash flow, and thus the Fund could be forced to liquidate securities at an inopportune time in order to generate cash to distribute to shareholders as required by tax laws. Fund Level and Other Risks: Anti-Takeover Provisions. The Declaration of Trust and the Fund’s by-laws open-end Counterparty Risk. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives or other transactions supported by another party’s credit will affect the value of those instruments. Certain entities that have served as counterparties in the markets for these transactions have incurred or may incur in the future significant financial hardships including bankruptcy and losses as a result of exposure to sub-prime Cybersecurity Risk. The Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund. Economic and Political Events Risk. The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the municipal securities of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the creditworthiness and value of such municipal securities. Fund Tax Risk. The Fund has elected to be treated and intends to qualify each year as a Regulated Investment Company (“RIC”) under the Internal Revenue Code of 1986, as amended (the “Code”). As a RIC, the Fund is not expected to be subject to U.S. federal income tax to the extent that it distributes its investment company taxable income and net capital gains. To qualify for the special tax treatment available to a RIC, the Fund must comply with certain investment, distribution, and diversification requirements. Under certain circumstances, the Fund may be forced to sell certain assets when it is not advantageous in order to meet these requirements, which may reduce the Fund’s overall return. If the Fund fails to meet any of these requirements, subject to the opportunity to cure such failures under applicable provisions of the Code, the Fund’s income would be subject to a double level of U.S. federal income tax. The Fund’s income, including its net capital gain, would first be subject to U.S. federal income tax at regular corporate rates, even if such income were distributed to shareholders and, second, all distributions by the Fund from earnings and profits, including distributions of net capital gain (if any), would be taxable to shareholders as dividends. Global Economic Risk. National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and asset prices around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies like China’s, may have global negative economic and market repercussions. Additionally, instability in various countries, such as Afghanistan and Syria, war, natural and environmental disasters, the spread of infectious illnesses or other public health emergencies , terrorist attacks in the United States and around the world, growing social and political discord in the United States, the European debt crisis, the response of the international community—through economic sanctions and otherwise—to international events, further downgrade of U.S. government securities, changes in the U.S. president or political shifts in Congress and other similar events may adversely affect the global economy and the markets and issuers in which the Fund invests. Recent examples of such events include Hamas’ attack on Israel in October 2023 and the ensuing conflict, the outbreak of a novel coronavirus known as COVID-19 sub-adviser, The Fund does not know and cannot predict how long the securities markets may be affected by these events, and the future impact of these and similar events on the global economy and securities markets is uncertain. The Fund may be adversely affected by abrogation of international agreements and national laws which have created the market instruments in which the Fund may invest, failure of the designated national and international authorities to enforce compliance with the same laws and agreements, failure of local, national and international organizations to carry out the duties prescribed to them under the relevant agreements, revisions of these laws and agreements which dilute their effectiveness or conflicting interpretation of provisions of the same laws and agreements. Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. Investment and Market Risk. An investment in common shares is subject to investment risk, including the possible loss of the entire principal amount that you invest. Common shares frequently trade at a discount to their NAV. An investment in common shares represents an indirect investment in the securities owned by the Fund. Common shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of Fund dividends and distributions. Legislation and Regulatory Risk. At any time after the date of this report, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, securities held by the Fund or the issuers of such securities. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objectives. Leverage Risk. The use of leverage creates special risks for common shareholders, including potential interest rate risks and the likelihood of greater volatility of NAV and market price of, and distributions on, the common shares. The use of leverage in a declining market will likely cause a greater decline in the Fund’s NAV, which may result at a greater decline of the common share price, than if the Fund were not to have used leverage. The Fund will pay (and common shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the Fund’s NAV. The investment adviser may, based on its assessment of market conditions and composition of the Fund’s holdings, increase or decrease the amount of leverage. Such changes may impact the Fund’s distributions and the price of the common shares in the secondary market. There is no assurance that the Fund’s use of leverage will be successful. The Fund may seek to refinance its leverage over time, in the ordinary course, as current forms of leverage mature or it is otherwise desirable to refinance; however, the form that such leverage will take cannot be predicted at this time. If the Fund is unable to replace existing leverage on comparable terms, its costs of leverage will increase. Accordingly, there is no assurance that the use of leverage may result in a higher yield or return to common shareholders. The amount of fees paid to the investment adviser and the sub-adviser sub-adviser Market Discount from Net Asset Value. Shares of closed-end closed-end Recent Market Conditions. Ukraine has experienced ongoing military conflict, most recently in February 2022 when Russia invaded Ukraine; this conflict may expand and military attacks could occur elsewhere in Europe. Europe has also been struggling with mass migration from the Middle East and Africa. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. Additionally, in October 2023 armed conflict broke out between Israel and the militant group Hamas after Hamas infiltrated Israel’s southern border from the Gaza Strip. Israel has since declared war against Hamas and this conflict has escalated into a greater regional conflict. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. The ongoing trade war between China and the United States, including the imposition of tariffs by each country on the other country’s products, has created a tense political environment. These actions may trigger a significant reduction in international trade, the oversupply of certain manufactured goods, substantial price reductions of goods and possible failure of individual companies and/or large segments of China’s export industry, which could have a negative impact on the Fund’s performance. U.S. companies that source material and goods from China and those that make large amounts of sales in China would be particularly vulnerable to an escalation of trade tensions. Uncertainty regarding the outcome of the trade tensions and the potential for a trade war could cause the U.S. dollar to decline against safe haven currencies, such as the Japanese yen and the euro. Events such as these and their consequences are difficult to predict and it is unclear whether further tariffs may be imposed or other escalating actions may be taken in the future. The U.S. Federal Reserve (the “Fed”) has in the past sharply raised interest rates and has signaled an intention to maintain higher interest rates until current inflation levels re-align The impact of these dev | |||||||||||||||||
| Effects of Leverage [Text Block] | EFFECTS OF LEVERAGE The following table is furnished in response to requirements of the SEC. It is designed to illustrate the effects of leverage through the use of senior securities, as that term is defined under Section 18 of the 1940 Act, as well as certain other forms of leverage, such as reverse repurchase agreements and investments in inverse floating rate securities, on common share total return, assuming investment portfolio total returns (consisting of income and changes in the value of investments held in the Fund’s portfolio) of -10%, -5%, The numbers are merely estimates, used for illustration. The costs of leverage may vary frequently and may be significantly higher or lower than the estimated rate. The assumed investment portfolio returns in the table below are hypothetical figures and are not necessarily indicative of the investment portfolio returns experienced or expected to be experienced by the Fund. Your actual returns may be greater or less than those appearing below. NBB Estimated Leverage as a Percentage of Managed Assets (Including Assets Attributable to Leverage) 40.55% Estimated Annual Effective Leverage Expense Rate Payable by Fund on Leverage 5.49% Annual Return Fund Portfolio Must Experience (net of expenses) to Cover Estimated Annual Effective Interest Expense Rate on Leverage 2.23% Common Share Total Return for (10.00)% Assumed Portfolio Total Return (20.56)% Common Share Total Return for (5.00)% Assumed Portfolio Total Return (12.15)% Common Share Total Return for 0.00% Assumed Portfolio Total Return (3.74)% Common Share Total Return for 5.00% Assumed Portfolio Total Return 4.67% Common Share Total Return for 10.00% Assumed Portfolio Total Return 13.08% Common Share total return is composed of two elements — the distributions paid by the Fund to holders of common shares (the amount of which is largely determined by the net investment income of the Fund after paying dividend payments on any preferred shares issued by the Fund and expenses on any forms of leverage outstanding) and gains or losses on the value of the securities and other instruments the Fund owns. As required by SEC rules, the table assumes that the Fund is more likely to suffer capital losses than to enjoy capital appreciation. For example, to assume a total return of 0%, the Fund must assume that the income it receives on its investments is entirely offset by losses in the value of those investments. This table reflects hypothetical performance of the Fund’s portfolio and not the actual performance of the Fund’s common shares, the value of which is determined by market forces and other factors. Should the Fund elect to add additional leverage to its portfolio, any benefits of such additional leverage cannot be fully achieved until the proceeds resulting from the use of such leverage have been received by the Fund and invested in accordance with the Fund’s investment objectives and policies. As noted above, the Fund’s willingness to use additional leverage, and the extent to which leverage is used at any time, will depend on many factors. | |||||||||||||||||
| Annual Interest Rate [Percent] | 40.55% | |||||||||||||||||
| Annual Interest Rate, Current [Percent] | 5.49% | |||||||||||||||||
| Annual Coverage Return Rate [Percent] | 2.23% | |||||||||||||||||
| Effects of Leverage [Table Text Block] | The numbers are merely estimates, used for illustration. The costs of leverage may vary frequently and may be significantly higher or lower than the estimated rate. The assumed investment portfolio returns in the table below are hypothetical figures and are not necessarily indicative of the investment portfolio returns experienced or expected to be experienced by the Fund. Your actual returns may be greater or less than those appearing below. NBB Estimated Leverage as a Percentage of Managed Assets (Including Assets Attributable to Leverage) 40.55% Estimated Annual Effective Leverage Expense Rate Payable by Fund on Leverage 5.49% Annual Return Fund Portfolio Must Experience (net of expenses) to Cover Estimated Annual Effective Interest Expense Rate on Leverage 2.23% Common Share Total Return for (10.00)% Assumed Portfolio Total Return (20.56)% Common Share Total Return for (5.00)% Assumed Portfolio Total Return (12.15)% Common Share Total Return for 0.00% Assumed Portfolio Total Return (3.74)% Common Share Total Return for 5.00% Assumed Portfolio Total Return 4.67% Common Share Total Return for 10.00% Assumed Portfolio Total Return 13.08% Common Share total return is composed of two elements — the distributions paid by the Fund to holders of common shares (the amount of which is largely determined by the net investment income of the Fund after paying dividend payments on any preferred shares issued by the Fund and expenses on any forms of leverage outstanding) and gains or losses on the value of the securities and other instruments the Fund owns. As required by SEC rules, the table assumes that the Fund is more likely to suffer capital losses than to enjoy capital appreciation. For example, to assume a total return of 0%, the Fund must assume that the income it receives on its investments is entirely offset by losses in the value of those investments. This table reflects hypothetical performance of the Fund’s portfolio and not the actual performance of the Fund’s common shares, the value of which is determined by market forces and other factors. Should the Fund elect to add additional leverage to its portfolio, any benefits of such additional leverage cannot be fully achieved until the proceeds resulting from the use of such leverage have been received by the Fund and invested in accordance with the Fund’s investment objectives and policies. As noted above, the Fund’s willingness to use additional leverage, and the extent to which leverage is used at any time, will depend on many factors. | |||||||||||||||||
| Return at Minus Ten [Percent] | (20.56%) | |||||||||||||||||
| Return at Minus Five [Percent] | (12.15%) | |||||||||||||||||
| Return at Zero [Percent] | (3.74%) | |||||||||||||||||
| Return at Plus Five [Percent] | 4.67% | |||||||||||||||||
| Return at Plus Ten [Percent] | 13.08% | |||||||||||||||||
| Effects of Leverage, Purpose [Text Block] | The following table is furnished in response to requirements of the SEC. It is designed to illustrate the effects of leverage through the use of senior securities, as that term is defined under Section 18 of the 1940 Act, as well as certain other forms of leverage, such as reverse repurchase agreements and investments in inverse floating rate securities, on common share total return, assuming investment portfolio total returns (consisting of income and changes in the value of investments held in the Fund’s portfolio) of -10%, -5%, | |||||||||||||||||
| Share Price [Table Text Block] | The following table shows for the periods indicated: (i) the high and low sales prices for the Common Shares reported as of the end of the day on the NYSE, (ii) the high and low net asset value (NAV) of the Common Shares, and (iii) the high and low of the premium/(discount) to NAV (expressed as a percentage) of shares of the Common Shares. Market Price NAV Premium/(Discount) Fiscal Quarter End High Low High Low High Low March 2024 $16.20 $15.21 $17.42 $16.55 (4.26)% (8.86)% December 2023 $15.98 $13.75 $17.57 $15.34 (6.98)% (10.86)% September 2023 $15.71 $14.21 $16.98 $16.01 (6.24)% (11.24)% June 2023 $16.56 $15.14 $17.30 $16.60 (3.50)% (9.42)% March 2023 $17.01 $15.76 $17.39 $16.27 (0.77)% (6.36)% December 2022 $16.66 $14.72 $16.93 $15.30 0.06% (6.15)% September 2022 $18.72 $15.37 $18.44 $16.24 3.69% (6.22)% June 2022 $19.88 $16.35 $19.99 $17.34 2.89% (7.84)% The following table shows, as of March 31, 2024 the Fund’s: (i) NAV per Common Share, (ii) market price, (iii) percentage of premium/(discount) to NAV per Common Share and, (iv) net assets attributable to Common Shares. March 31, 2024 NAV per Common Share $ 16.81 Market Price $ 15.32 Percentage of Premium/(Discount) to NAV per Common Share (8.86)% Net Assets Attributable to Common Shares $ 493,978,877 Shares of closed-end open-end | |||||||||||||||||
| Below Investment Grade Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Below Investment Grade Risk. Municipal securities of below investment grade quality are regarded as having speculative characteristics with respect to the issuer’s capacity to pay dividends or interest and repay principal, and may be subject to higher price volatility and default risk than investment grade municipal securities of comparable terms and duration. Issuers of lower grade municipal securities may be highly leveraged and may not have available to them more traditional methods of financing. The prices of these lower grade securities are typically more sensitive to negative developments, such as a decline in the issuer’s revenues or a general economic downturn. The secondary market for lower rated municipal securities may not be as liquid as the secondary market for more highly rated municipal securities, a factor which may have an adverse effect on the Fund’s ability to dispose of a particular municipal security. If a below investment grade municipal security goes into default, or its issuer enters bankruptcy, it might be difficult to sell that security in a timely manner at a reasonable price. | |||||||||||||||||
| Build America Bonds BABs Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Build America Bonds (“BABs”) Risk. BABs are taxable municipal obligations issued pursuant to the American Recovery and Reinvestment Act of 2009 that are subject to federal subsidies of up to 35% of the interest payable on the bonds in the form of direct subsidies to the bond issuer or refundable tax credits to the bond holder. BABs are not guaranteed by the U.S. government or its agencies or instrumentalities. While the federal subsidy continues for the life of the bonds, provided that the issuer continues to meet all applicable program eligibility requirements, there is no assurance that the federal subsidy will be continued at original levels. Under the sequestration process under the Budget Control Act of 2011, automatic spending cuts that became effective on March 1, 2013 reduced the federal subsidy for BABs and other subsidized taxable municipal bonds. The reduced federal subsidy has been extended through 2030. The subsidy payments were reduced by 6.6% in 2018 and 6.2% in 2019, 5.9% in 2020 and 5.7% between 2021 and 2030. Further decreases in the level of the subsidy may impair the ability of issuers to make interest payments when due. BABs were an alternative form of financing to state and local governments whose primary means for accessing the capital markets had been through issuance of tax free municipal bonds. Pursuant to the terms of the American Recovery and Reinvestment Act of 2009, the issuance of BABs ceased on December 31, 2010. As a result, the availability of such bonds is limited and there can be no assurance that BABs will be actively traded. The market for the bonds and/or their liquidity may be negatively affected. Changes to the U.S. federal income tax laws or other federal legislation may affect the demand for and supply of taxable municipal bonds, including BABs, and/or trigger extraordinary call features of the BABs. The extraordinary call features of certain BABs permit early redemption at par value, which, if triggered, could result in potential losses for the Fund if such BABs were purchased at prices above par, and may require the Fund to reinvest redemption proceeds in lower-yielding securities. BABs involve similar risks as traditional municipal bonds, including credit, call and market risk. Because certain states, including California, New York, Illinois, Texas and Ohio, were heavy issuers of BABs, the Fund may have a greater exposure to the economic or other factors affecting such states than a more diversified national municipal bond fund. In addition, should a BAB’s issuer fail to continue to meet the applicable requirements, it is possible that such issuer may not receive federal cash subsidy payments, impairing the issuer’s ability to make scheduled interest payments. BABs may be subject to greater reinvestment risk, which is the risk that the Fund is unable to invest in bonds with similar yields, as BABs with attractive above-market purchase yields mature or are called. | |||||||||||||||||
| Call Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Call Risk. | |||||||||||||||||
| Credit Risks [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Credit Risk. Issuers of municipal securities in which the Fund may invest may default on their obligations to pay principal or interest when due. This non-payment non-payment | |||||||||||||||||
| Credit Spread Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Credit Spread Risk. | |||||||||||||||||
| Defaulted or Distressed Securities Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Defaulted or Distressed Securities Risk. Investments in “distressed” securities, meaning those whose issuers are experiencing financial difficulties or distress at the time of acquisition, present a substantial risk of future default. In the event distressed securities become defaulted securities or the Fund otherwise holds defaulted securities, the Fund may incur losses, including additional expenses, to the extent it is required to seek recovery upon a default in the payment of principal or interest on those securities. In any reorganization or liquidation proceeding relating to a portfolio security, the Fund may lose its entire investment or may be required to accept cash or securities with a value less than its original investment. Defaulted or distressed securities may be subject to restrictions on resale. | |||||||||||||||||
| Deflation Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Deflation Risk. Deflation risk is the risk that prices throughout the economy decline over time. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio. | |||||||||||||||||
| Derivatives Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Derivatives Risk. The use of derivatives involves additional risks and transaction costs which could leave the Fund in a worse position than if it had not used these instruments. Derivative instruments can be used to acquire or to transfer the risk and returns of a municipal security or other asset without buying or selling the municipal security or asset. These instruments may entail investment exposures that are greater than their cost would suggest. As a result, a small investment in derivatives can result in losses that greatly exceed the original investment. Derivatives can be highly volatile, illiquid and difficult to value. An over-the-counter It is possible that regulatory or other developments in the derivatives market, including changes in government regulation, could adversely impact the Fund’s ability to invest in certain derivatives or successfully use derivative instruments. | |||||||||||||||||
| Duration Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Duration Risk. | |||||||||||||||||
| Economic Sector Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Economic Sector Risk. The Fund may invest a significant amount of its total assets in municipal securities in the same economic sector. This may make the Fund more susceptible to adverse economic, political or regulatory occurrences affecting an economic sector making the Fund more vulnerable to unfavorable developments in that sector than funds that invest more broadly. As the percentage of the Fund’s Managed Assets invested in a particular sector increases, so does the potential for fluctuation in the value of the Fund’s assets. In addition, the Fund may invest a significant portion of its assets in certain sectors of the municipal securities market, such as health care facilities, private educational facilities, special taxing districts and start-up | |||||||||||||||||
| Financial Futures and Options Transactions Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Financial Futures and Options Transactions Risk. The Fund may use certain transactions for hedging the portfolio’s exposure to credit risk and the risk of increases in interest rates, which could result in poorer overall performance for the Fund. There may be an imperfect correlation between price movements of the futures and options and price movements of the portfolio securities being hedged. If the Fund engages in futures transactions or in the writing of options on futures, it will be required to maintain initial margin and maintenance margin and may be required to make daily variation margin payments in accordance with applicable rules of the exchanges and the Commodity Futures Trading Commission (“CFTC”). If the Fund purchases a financial futures contract or a call option or writes a put option in order to hedge the anticipated purchase of municipal securities, and if the Fund fails to complete the anticipated purchase transaction, the Fund may have a loss or a gain on the futures or options transaction that will not be offset by price movements in the municipal securities that were the subject of the anticipatory hedge. There can be no assurance that a liquid market will exist at a time when the Fund seeks to close out a derivatives or futures or a futures option position, and the Fund would remain obligated to meet margin requirements until the position is closed. | |||||||||||||||||
| Hedging Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Hedging Risk. sub-adviser’s sub-adviser’s | |||||||||||||||||
| Illiquid Investments Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Illiquid Investments Risk. Illiquid investments are investments that are not readily marketable. These investments may include restricted investments, including Rule 144A securities, which cannot be resold to the public without an effective registration statement under the 1933 Act, or if they are unregistered may be sold only in a privately negotiated transaction or pursuant to an available exemption from registration. The Fund may not be able to readily dispose of such investments at prices that approximate those at which the Fund could sell such investments if they were more widely traded and, as a result of such illiquidity, the Fund may have to sell other investments or engage in borrowing transactions if necessary to raise cash to meet its obligations. Limited liquidity can also affect the market price of investments, thereby adversely affecting the Fund’s NAV and ability to make dividend distributions. The financial markets in general have in recent years experienced periods of extreme secondary market supply and demand imbalance, resulting in a loss of liquidity during which market prices were suddenly and substantially below traditional measures of intrinsic value. During such periods, some investments could be sold only at arbitrary prices and with substantial losses. Periods of such market dislocation may occur again at any time. | |||||||||||||||||
| Income Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Income Risk. The Fund’s income could decline due to falling market interest rates. This is because, in a falling interest rate environment, the Fund generally will have to invest the proceeds from maturing portfolio securities in lower-yielding securities. | |||||||||||||||||
| Interest Rate Risks [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Interest Rate Risk. Interest rate risk is the risk that municipal securities in the Fund’s portfolio will decline in value because of changes in market interest rates. Generally, when market interest rates rise, the market value of such securities will fall, and vice versa. As interest rates decline, issuers of municipal securities may prepay principal earlier than scheduled, forcing the Fund to reinvest in lower-yielding securities and potentially reducing the Fund’s income. As interest rates increase, slower than expected principal payments may extend the average life of municipal securities, potentially locking in a below-market interest rate and reducing the Fund’s value. In typical market interest rate environments, the prices of longer-term municipal securities generally fluctuate more than prices of shorter-term municipal securities as interest rates change. | |||||||||||||||||
| Inverse Floating Rate Securities Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Inverse Floating Rate Securities Risk. The Fund may invest in inverse floating rate securities. In general, income on inverse floating rate securities will decrease when short-term interest rates increase and increase when short-term interest rates decrease. Investments in inverse floating rate securities may subject the Fund to the risks of reduced or eliminated interest payments and losses of principal. In addition, inverse floating rate securities may increase or decrease in value at a greater rate than the underlying interest rate, which effectively leverages the Fund’s investment. As a result, the market value of such securities generally will be more volatile than that of fixed rate securities. The Fund may invest in inverse floating rate securities issued by special purpose trusts that have recourse to the Fund. In such instances, the Fund may be at risk of loss that exceeds its investment in the inverse floating rate securities. The Fund may be required to sell its inverse floating rate securities at less than favorable prices, or liquidate other Fund portfolio holdings in certain circumstances, including, but not limited to, the following: · If the Fund has a need for cash and the securities in a special purpose trust are not actively trading due to adverse market conditions; · If special purpose trust sponsors (as a collective group or individually) experience financial hardship and consequently seek to terminate their respective outstanding special purpose trusts; and · If the value of an underlying security declines significantly and if additional collateral has not been posted by the Fund. | |||||||||||||||||
| Municipal Securities Market Liquidity Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Municipal Securities Market Liquidity Risk. Inventories of municipal securities held by brokers and dealers have decreased in recent years, lessening their ability to make a market in these securities. This reduction in market making capacity has the potential to decrease the Fund’s ability to buy or sell municipal securities at attractive prices, and increase municipal security price volatility and trading costs, particularly during periods of economic or market stress. In addition, recent federal banking regulations may cause certain dealers to reduce their inventories of municipal securities, which may further decrease the Fund’s ability to buy or sell municipal securities. As a result, the Fund may be forced to accept a lower price to sell a security, to sell other securities to raise cash, or to give up an investment opportunity, any of which could have a negative effect on performance. If the Fund needed to sell large blocks of municipal securities to raise cash to meet its obligations, those sales could further reduce the municipal securities’ prices and hurt performance. | |||||||||||||||||
| Municipal Securities Market Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Municipal Securities Market Risk. The amount of public information available about the municipal securities in the Fund’s portfolio is generally less than that for corporate equities or bonds, and the investment performance of the Fund may therefore be more dependent on the analytical abilities of the sub-adviser | |||||||||||||||||
| Other Investment Companies Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Other Investment Companies Risk. The Fund may invest in the securities of other investment companies, including ETFs. Investing in an investment company exposes the Fund to all of the risks of that investment company’s investments. The Fund, as a holder of the securities of other investment companies, will bear its pro rata portion of the other investment companies’ expenses, including advisory fees. These expenses are in addition to the direct expenses of the Fund’s own operations. As a result, the cost of investing in investment company shares may exceed the costs of investing directly in its underlying investments. In addition, securities of other investment companies may be leveraged. As a result, the Fund may be indirectly exposed to leverage through an investment in such securities and therefore magnify the Fund’s leverage risk. With respect to ETF’s, an ETF that is based on a specific index may not be able to replicate and maintain exactly the composition and relative weighting of securities in the index. The value of an ETF based on a specific index is subject to change as the values of its respective component assets fluctuate according to market volatility. ETFs typically rely on a limited pool of authorized participants to create and redeem shares, and an active trading market for ETF shares may not develop or be maintained. The market value of shares of ETFs and closed-end | |||||||||||||||||
| Reinvestment Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Reinvestment Risk. Reinvestment risk is the risk that income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called municipal securities at market interest rates that are below the portfolio’s current earnings rate. A decline in income could affect the common shares’ market price, NAV and/or a common shareholder’s overall returns. | |||||||||||||||||
| Special Risks Related to Certain Municipal Obligations [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Special Risks Related to Certain Municipal Obligations. Municipal leases and certificates of participation involve special risks not normally associated with general obligations or revenue bonds. Leases and installment purchase or conditional sale contracts (which normally provide for title to the leased asset to pass eventually to the governmental issuer) have evolved as a means for governmental issuers to acquire property and equipment without meeting the constitutional and statutory requirements for the issuance of debt. The debt issuance limitations are deemed to be inapplicable because of the inclusion in many leases or contracts of “non-appropriation” non-appropriation non-appropriation, Certificates of participation involve the same risks as the underlying municipal leases. In addition, the Fund may be dependent upon the municipal authority issuing the certificates of participation to exercise remedies with respect to the underlying securities. Certificates of participation also entail a risk of default or bankruptcy, both of the issuer of the municipal lease and also the municipal agency issuing the certificate of participation. | |||||||||||||||||
| Swap Transactions Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Swap Transactions Risk. The Fund may enter into debt-related derivative instruments such as credit default swap contracts and interest rate swaps. Like most derivative instruments, the use of swaps is a highly specialized activity that involves investment techniques and risks different from those associated with ordinary portfolio securities transactions. In addition, the use of swaps requires an understanding by the investment adviser and/or the sub-adviser sub-adviser | |||||||||||||||||
| Unrated Securities Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Unrated Securities Risk. | |||||||||||||||||
| Valuation Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Valuation Risk. The municipal securities in which the Fund invests typically are valued by a pricing service utilizing a range of market-based inputs and assumptions, including readily available market quotations obtained from broker-dealers making markets in such instruments, cash flows and transactions for comparable instruments. There is no assurance that the Fund will be able to sell a portfolio security at the price established by the pricing service, which could result in a loss to the Fund. Pricing services generally price municipal securities assuming orderly transactions of an institutional “round lot” size, but some trades may occur in smaller, “odd lot” sizes, often at lower prices than institutional round lot trades. Different pricing services may incorporate different assumptions and inputs into their valuation methodologies, potentially resulting in different values for the same securities. As a result, if the Fund were to change pricing services, or if the Fund’s pricing service were to change its valuation methodology, there could be a material impact, either positive or negative, on the Fund’s NAV. | |||||||||||||||||
| Zero Coupon Bonds Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Zero Coupon Bonds Risk. Because interest on zero coupon bonds is not paid on a current basis, the values of zero coupon bonds will be more volatile in response to interest rate changes than the values of bonds that distribute income regularly. Although zero coupon bonds generate income for accounting purposes, they do not produce cash flow, and thus the Fund could be forced to liquidate securities at an inopportune time in order to generate cash to distribute to shareholders as required by tax laws. | |||||||||||||||||
| AntiTakeover Provisions [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Anti-Takeover Provisions. The Declaration of Trust and the Fund’s by-laws open-end | |||||||||||||||||
| Counterparty Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Counterparty Risk. Changes in the credit quality of the companies that serve as the Fund’s counterparties with respect to derivatives or other transactions supported by another party’s credit will affect the value of those instruments. Certain entities that have served as counterparties in the markets for these transactions have incurred or may incur in the future significant financial hardships including bankruptcy and losses as a result of exposure to sub-prime | |||||||||||||||||
| Cybersecurity Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Cybersecurity Risk. The Fund and its service providers are susceptible to operational and information security risk resulting from cyber incidents. Cyber incidents refer to both intentional attacks and unintentional events including: processing errors, human errors, technical errors including computer glitches and system malfunctions, inadequate or failed internal or external processes, market-wide technical-related disruptions, unauthorized access to digital systems (through “hacking” or malicious software coding), computer viruses, and cyber-attacks which shut down, disable, slow or otherwise disrupt operations, business processes or website access or functionality (including denial of service attacks). Cyber incidents could adversely impact the Fund and cause the Fund to incur financial loss and expense, as well as face exposure to regulatory penalties, reputational damage, and additional compliance costs associated with corrective measures. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future. Furthermore, the Fund cannot control the cybersecurity plans and systems put in place by its service providers or any other third parties whose operations may affect the Fund. | |||||||||||||||||
| Economic and Political Events Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Economic and Political Events Risk. The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the municipal securities of similar projects (such as those relating to the education, health care, housing, transportation, or utilities industries), industrial development bonds, or in particular types of municipal securities (such as general obligation bonds, private activity bonds or moral obligation bonds). Such developments may adversely affect a specific industry or local political and economic conditions, and thus may lead to declines in the creditworthiness and value of such municipal securities. | |||||||||||||||||
| Fund Tax Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Fund Tax Risk. The Fund has elected to be treated and intends to qualify each year as a Regulated Investment Company (“RIC”) under the Internal Revenue Code of 1986, as amended (the “Code”). As a RIC, the Fund is not expected to be subject to U.S. federal income tax to the extent that it distributes its investment company taxable income and net capital gains. To qualify for the special tax treatment available to a RIC, the Fund must comply with certain investment, distribution, and diversification requirements. Under certain circumstances, the Fund may be forced to sell certain assets when it is not advantageous in order to meet these requirements, which may reduce the Fund’s overall return. If the Fund fails to meet any of these requirements, subject to the opportunity to cure such failures under applicable provisions of the Code, the Fund’s income would be subject to a double level of U.S. federal income tax. The Fund’s income, including its net capital gain, would first be subject to U.S. federal income tax at regular corporate rates, even if such income were distributed to shareholders and, second, all distributions by the Fund from earnings and profits, including distributions of net capital gain (if any), would be taxable to shareholders as dividends. | |||||||||||||||||
| Investment and Market Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Investment and Market Risk. An investment in common shares is subject to investment risk, including the possible loss of the entire principal amount that you invest. Common shares frequently trade at a discount to their NAV. An investment in common shares represents an indirect investment in the securities owned by the Fund. Common shares at any point in time may be worth less than your original investment, even after taking into account the reinvestment of Fund dividends and distributions. | |||||||||||||||||
| Legislation and Regulatory Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Legislation and Regulatory Risk. At any time after the date of this report, legislation or additional regulations may be enacted that could negatively affect the assets of the Fund, securities held by the Fund or the issuers of such securities. Fund shareholders may incur increased costs resulting from such legislation or additional regulation. There can be no assurance that future legislation, regulation or deregulation will not have a material adverse effect on the Fund or will not impair the ability of the Fund to achieve its investment objectives. | |||||||||||||||||
| Leverage Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Leverage Risk. The use of leverage creates special risks for common shareholders, including potential interest rate risks and the likelihood of greater volatility of NAV and market price of, and distributions on, the common shares. The use of leverage in a declining market will likely cause a greater decline in the Fund’s NAV, which may result at a greater decline of the common share price, than if the Fund were not to have used leverage. The Fund will pay (and common shareholders will bear) any costs and expenses relating to the Fund’s use of leverage, which will result in a reduction in the Fund’s NAV. The investment adviser may, based on its assessment of market conditions and composition of the Fund’s holdings, increase or decrease the amount of leverage. Such changes may impact the Fund’s distributions and the price of the common shares in the secondary market. There is no assurance that the Fund’s use of leverage will be successful. The Fund may seek to refinance its leverage over time, in the ordinary course, as current forms of leverage mature or it is otherwise desirable to refinance; however, the form that such leverage will take cannot be predicted at this time. If the Fund is unable to replace existing leverage on comparable terms, its costs of leverage will increase. Accordingly, there is no assurance that the use of leverage may result in a higher yield or return to common shareholders. The amount of fees paid to the investment adviser and the sub-adviser sub-adviser | |||||||||||||||||
| 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 closed-end | |||||||||||||||||
| Recent Market Conditions [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Recent Market Conditions. Ukraine has experienced ongoing military conflict, most recently in February 2022 when Russia invaded Ukraine; this conflict may expand and military attacks could occur elsewhere in Europe. Europe has also been struggling with mass migration from the Middle East and Africa. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. Additionally, in October 2023 armed conflict broke out between Israel and the militant group Hamas after Hamas infiltrated Israel’s southern border from the Gaza Strip. Israel has since declared war against Hamas and this conflict has escalated into a greater regional conflict. The ultimate effects of these events and other socio-political or geographical issues are not known but could profoundly affect global economies and markets. The ongoing trade war between China and the United States, including the imposition of tariffs by each country on the other country’s products, has created a tense political environment. These actions may trigger a significant reduction in international trade, the oversupply of certain manufactured goods, substantial price reductions of goods and possible failure of individual companies and/or large segments of China’s export industry, which could have a negative impact on the Fund’s performance. U.S. companies that source material and goods from China and those that make large amounts of sales in China would be particularly vulnerable to an escalation of trade tensions. Uncertainty regarding the outcome of the trade tensions and the potential for a trade war could cause the U.S. dollar to decline against safe haven currencies, such as the Japanese yen and the euro. Events such as these and their consequences are difficult to predict and it is unclear whether further tariffs may be imposed or other escalating actions may be taken in the future. The U.S. Federal Reserve (the “Fed”) has in the past sharply raised interest rates and has signaled an intention to maintain higher interest rates until current inflation levels re-align The impact of these developments in the near- and long-term is unknown and could have additional adverse effects on economies, financial markets and asset valuations around the world. | |||||||||||||||||
| Reverse Repurchase Agreement Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Reverse Repurchase Agreement Risk. A reverse repurchase agreement, in economic essence, constitutes a securitized borrowing by the Fund from the security purchaser. The Fund may enter into reverse repurchase agreements for the purpose of creating a leveraged investment exposure and, as such, their usage involves essentially the same risks associated with a leveraging strategy generally since the proceeds from these agreements may be invested in additional portfolio securities. Reverse repurchase agreements tend to be short-term in tenor, and there can be no assurances that the purchaser (lender) will commit to extend or “roll” a given agreement upon its agreed-upon repurchase date or an alternative purchaser can be identified on similar terms. Reverse repurchase agreements also involve the risk that the purchaser fails to return the securities as agreed upon, files for bankruptcy or becomes insolvent. The Fund may be restricted from taking normal portfolio actions during such time, could be subject to loss to the extent that the proceeds of the agreement are less than the value of securities subject to the agreement and may experience adverse tax consequences. | |||||||||||||||||
| Inflation Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Inflation Risk. Inflation risk is the risk that the value of assets or income from investments will be worth less in the future as inflation decreases the value of money. As inflation increases, the real value of the common shares and distributions can decline. Currently, inflation rates are elevated relative to normal market conditions and could increase. | |||||||||||||||||
| Insurance Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Insurance Risk. The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub-prime | |||||||||||||||||
| Global Economic Risk [Member] | ||||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Risk [Text Block] | Global Economic Risk. National and regional economies and financial markets are becoming increasingly interconnected, which increases the possibilities that conditions in one country, region or market might adversely impact issuers in a different country, region or market. Changes in legal, political, regulatory, tax and economic conditions may cause fluctuations in markets and asset prices around the world, which could negatively impact the value of the Fund’s investments. Major economic or political disruptions, particularly in large economies like China’s, may have global negative economic and market repercussions. Additionally, instability in various countries, such as Afghanistan and Syria, war, natural and environmental disasters, the spread of infectious illnesses or other public health emergencies , terrorist attacks in the United States and around the world, growing social and political discord in the United States, the European debt crisis, the response of the international community—through economic sanctions and otherwise—to international events, further downgrade of U.S. government securities, changes in the U.S. president or political shifts in Congress and other similar events may adversely affect the global economy and the markets and issuers in which the Fund invests. Recent examples of such events include Hamas’ attack on Israel in October 2023 and the ensuing conflict, the outbreak of a novel coronavirus known as COVID-19 sub-adviser, The Fund does not know and cannot predict how long the securities markets may be affected by these events, and the future impact of these and similar events on the global economy and securities markets is uncertain. The Fund may be adversely affected by abrogation of international agreements and national laws which have created the market instruments in which the Fund may invest, failure of the designated national and international authorities to enforce compliance with the same laws and agreements, failure of local, national and international organizations to carry out the duties prescribed to them under the relevant agreements, revisions of these laws and agreements which dilute their effectiveness or conflicting interpretation of provisions of the same laws and agreements. Governmental and quasi-governmental authorities and regulators throughout the world have in the past responded to major economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or quick reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. | |||||||||||||||||
| Common Shares [Member] | ||||||||||||||||||
| Other Annual Expenses [Abstract] | ||||||||||||||||||
| Basis of Transaction Fees, Note [Text Block] | As a Percentage of Net Assets Attributable to Common Shares | |||||||||||||||||
| General Description of Registrant [Abstract] | ||||||||||||||||||
| Lowest Price or Bid | 15.21 | $ 13.75 | $ 14.21 | $ 15.14 | 15.76 | $ 14.72 | $ 15.37 | $ 16.35 | ||||||||||
| Highest Price or Bid | 16.2 | 15.98 | 15.71 | 16.56 | 17.01 | 16.66 | 18.72 | 19.88 | ||||||||||
| Lowest Price or Bid, NAV | 16.55 | 15.34 | 16.01 | 16.6 | 16.27 | 15.3 | 16.24 | 17.34 | ||||||||||
| Highest Price or Bid, NAV | $ 17.42 | $ 17.57 | $ 16.98 | $ 17.3 | $ 17.39 | $ 16.93 | $ 18.44 | $ 19.99 | ||||||||||
| Highest Price or Bid, Premium (Discount) to NAV [Percent] | (4.26%) | (6.98%) | (6.24%) | (3.50%) | (0.77%) | 0.06% | 3.69% | 2.89% | ||||||||||
| Lowest Price or Bid, Premium (Discount) to NAV [Percent] | (8.86%) | (10.86%) | (11.24%) | (9.42%) | (6.36%) | (6.15%) | (6.22%) | (7.84%) | ||||||||||
| Share Price | $ 15.32 | $ 15.32 | ||||||||||||||||
| NAV Per Share | $ 16.81 | $ 16.81 | ||||||||||||||||
| Latest Premium (Discount) to NAV [Percent] | (8.86%) | |||||||||||||||||
| Capital Stock, Long-Term Debt, and Other Securities [Abstract] | ||||||||||||||||||
| Outstanding Security, Title [Text Block] | Common shares | |||||||||||||||||
| Outstanding Security, Held [Shares] | 29,394,752 | |||||||||||||||||
| Interest And Other Related Expenses [Member] | ||||||||||||||||||
| Other Annual Expenses [Abstract] | ||||||||||||||||||
| Other Expenses, Note [Text Block] | Interest and Other Related Expenses reflect actual expenses and fees for leverage incurred by the Fund for the fiscal year ended March 31, 2024. The types of leverage used by the Fund during the fiscal year ended March 31, 2024 are described in the Fund Leverage and the Notes to Financial Statements sections of this annual report. Actual Interest and Other Related Expenses incurred in the future may be higher or lower. If short-term market interest rates rise in the future, and if the Fund continues to maintain leverage, the cost of which is tied to short-term interest rates, the Fund’s interest expenses on its short-term borrowings can be expected to rise in tandem. The Fund’s use of leverage will increase the amount of management fees paid to the Fund’s adviser and sub-advisor(s). | |||||||||||||||||
| [1]The maximum sales charge for offerings made at-the-market is 1.00%. If the Common Shares are sold to or through underwriters in an offering that is not made at-the-market, the applicable Prospectus Supplement will set forth any other applicable sales load and the estimated offering expenses. Fund shareholders will pay all offering expenses involved with an offering.[2]You will be charged a $2.50 service charge and pay brokerage charges if you direct Computershare Inc. and Computershare Trust Company, N.A., as agent for the common shareholders, to sell your Common Shares held in a dividend reinvestment account.[3]Stated as percentages of average net assets attributable to Common Shares for the fiscal year ended March 31, 2024.[4]Interest and Other Related Expenses reflect actual expenses and fees for leverage incurred by the Fund for the fiscal year ended March 31, 2024. The types of leverage used by the Fund during the fiscal year ended March 31, 2024 are described in the Fund Leverage and the Notes to Financial Statements sections of this annual report. Actual Interest and Other Related Expenses incurred in the future may be higher or lower. If short-term market interest rates rise in the future, and if the Fund continues to maintain leverage, the cost of which is tied to short-term interest rates, the Fund’s interest expenses on its short-term borrowings can be expected to rise in tandem. The Fund’s use of leverage will increase the amount of management fees paid to the Fund’s adviser and sub-advisor(s).[5]Other Expenses are based on estimated amounts for the current fiscal year. Expenses attributable to the Fund’s investments, if any, in other investment companies are currently estimated not to exceed 0.01%.[6]Aggregate Amount Outstanding: Aggregate amount outstanding represents the liquidation preference as of the end of the relevant fiscal year and does not include any preferred shares noticed for redemption as noted on the Statement of Assets and Liabilities where applicable.[7]Asset Coverage Per $1,000: Asset coverage per $1,000 is calculated by subtracting the Fund’s liabilities and indebtedness not represented by senior securities from the Fund’s total assets, dividing the result by the aggregate amount of the Fund’s senior securities representing indebtedness then outstanding (if applicable), plus the aggregate of the involuntary liquidation preference of the outstanding preferred shares, if applicable, and multiplying the result by 1,000. | ||||||||||||||||||
