S000010780 [Member] Investment Risks - S000010780 [Member] |
Apr. 30, 2025 |
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| Changing Distribution Level Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Changing Distribution Level Risk. The Fund normally expects to receive income which may include interest, dividends and/or capital gains, depending upon its investments. The distribution amounts paid by the Fund will vary and generally depend on the amount of income the Fund earns (less expenses) on its portfolio holdings, and capital gains or losses it recognizes. A decline in the Fund’s income or net capital gains arising from its investments may reduce its distribution level.
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| Counterparty Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Counterparty Risk. Counterparty risk is the risk that a counterparty to a transaction in a financial instrument held by the Fund or by a special purpose or structured vehicle invested in by the Fund may become insolvent or otherwise fail to perform its obligations. As a result, the Fund may obtain no or limited recovery of its investment, and any recovery may be significantly delayed.
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| Credit Risks [Member] | |
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| Risk [Text Block] | Credit Risk. Credit risk is the risk that the value of debt instruments may decline if the issuer thereof defaults or otherwise becomes unable or unwilling, or is perceived to be unable or unwilling, to honor its financial obligations, such as making payments to the Fund when due. Debt instruments backed by an issuer's taxing authority may be subject to legal limits on the issuer's power to increase taxes or otherwise to raise revenue, or may be dependent on legislative appropriation or government aid. Certain debt instruments are backed only by revenues derived from a particular project or source, rather than by an issuer's taxing authority, and thus may have a greater risk of default. Credit rating agencies, such as S&P Global Ratings, Moody’s Investors Service, Inc. (Moody’s Ratings), Fitch Ratings, Inc. (Fitch), Morningstar DBRS (DBRS) and Kroll Bond Rating Agency, LLC (KBRA), assign credit ratings to certain debt instruments to indicate their credit risk. A rating downgrade by such agencies can negatively impact the value of such instruments. Lower-rated or unrated instruments held by the Fund may present increased credit risk as compared to higher-rated instruments. Non-investment grade debt instruments may be subject to greater price fluctuations and are more likely to experience a default than investment grade debt instruments and therefore may expose the Fund to increased credit risk. If the Fund purchases unrated instruments, or if the ratings of instruments held by the Fund are lowered after purchase, the Fund will depend on analysis of credit risk more heavily than usual.
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| Derivatives Risks [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Derivatives Risk. Derivatives may involve significant risks. Derivatives are financial instruments with a value in relation to, or derived from, the value of an underlying asset(s) or other reference, such as an index, rate or other economic indicator (each an underlying reference). Derivatives may include those that are privately placed or otherwise exempt from SEC registration, including certain Rule 144A eligible securities. Derivatives could result in Fund losses if the underlying reference does not perform as anticipated. Use of derivatives is a highly specialized activity that can involve investment techniques, risks, and tax planning different from those associated with more traditional investment instruments. The Fund’s derivatives strategy may not be successful and use of certain derivatives could result in substantial, potentially unlimited, losses to the Fund regardless of the Fund’s actual investment. A relatively small movement in the price, rate or other economic indicator associated with the underlying reference may result in substantial losses for the Fund. Derivatives may be more volatile than other types of investments. The value of derivatives may be influenced by a variety of factors, including national and international political and economic developments. Potential changes to the regulation of the derivatives markets may make derivatives more costly, may limit the market for derivatives, or may otherwise adversely affect the value or performance of derivatives. Derivatives can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk and interest rate risk, while potentially exposing the Fund to counterparty risk, leverage risk and liquidity risk.
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| Derivatives Risk Futures Contracts Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Derivatives Risk – Futures Contracts Risk. A futures contract is an exchange-traded derivative transaction between two parties in which a buyer (holding the “long” position) agrees to pay a fixed price (or rate) at a specified future date for delivery of an underlying reference from a seller (holding the “short” position). The seller hopes that the market price on the delivery date is less than the agreed upon price, while the buyer hopes for the contrary. Certain futures contract markets are highly volatile, and futures contracts may be illiquid. Futures exchanges may limit fluctuations in futures contract prices by imposing a maximum permissible daily price movement. The Fund may be disadvantaged if it is prohibited from executing a trade outside the daily permissible price movement. At or prior to maturity of a futures contract, the Fund may enter into an offsetting contract and may incur a loss to the extent there has been adverse movement in futures contract prices. The liquidity of the futures markets depends on participants entering into offsetting transactions rather than making or taking delivery. To the extent participants make or take delivery, liquidity in the futures market could be reduced. Because of the low margin deposits normally required in futures trading, it is possible that the Fund may employ a high degree of leverage in the portfolio. As a result, a relatively small price movement in a futures contract may result in substantial losses to the Fund, exceeding the amount of the margin paid. For certain types of futures contracts, losses are potentially unlimited. Futures markets are highly volatile and the use of futures may increase the volatility of the Fund’s NAV. Futures contracts can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk and interest rate risk, while potentially exposing the Fund to counterparty risk, leverage risk and liquidity risk.
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| Derivatives Risk Inverse Floaters Risk [Member] | |
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| Risk [Text Block] | Derivatives Risk – Inverse Floaters Risk. Inverse variable or floating rate obligations, sometimes referred to as inverse floaters, are a type of over-the-counter derivative debt instrument with a variable or floating coupon rate that moves in the opposite direction of an underlying reference, typically short-term interest rates. While inverse floaters tend to provide more income than similar term and credit quality fixed-rate bonds, they also exhibit greater volatility in price movement, which could result in significant losses for the Fund. An inverse floater may have the effect of investment leverage to the extent that its coupon rate varies by a magnitude that exceeds the magnitude of the change in the index or reference rate of interest, which could result in increased losses for the Fund. Inverse floaters can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk and interest rate risk, while potentially exposing the Fund to counterparty risk, leverage risk and liquidity risk.
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| Derivatives Risk Swaps Risk [Member] | |
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| Risk [Text Block] | Derivatives Risk – Swaps Risk. In a typical swap transaction, two parties agree to exchange the return earned on a specified underlying reference for a fixed return or the return from another underlying reference during a specified period of time. Swaps may be difficult to value and may be illiquid. Swaps could result in Fund losses if the underlying asset or reference does not perform as anticipated. Swaps create significant investment leverage such that a relatively small price movement in a swap may result in immediate and substantial losses to the Fund. The Fund may only close out a swap with its particular counterparty, and may only transfer a position with the consent of that counterparty. Certain swaps, such as short swap transactions and total return swaps, have the potential for unlimited losses, regardless of the size of the initial position. Swaps can increase the Fund’s risk exposure to underlying references and their attendant risks, such as credit risk, market risk and interest rate risk, while potentially exposing the Fund to counterparty risk, leverage risk and liquidity risk. ■ A Municipal Market Data (MMD) Rate Lock permits a Fund to lock in a specific municipal interest rate for a portion of its portfolio to preserve a return on a particular investment or a portion of its portfolio, which in turn protects against any increase in the price of securities to be purchased at a later date. By using an MMD Rate Lock, the Fund can create a synthetic long or short duration position. A Fund will ordinarily use these transactions as a hedge or for duration or risk management, which may not be successful. An MMD Rate Lock is a contract between a Fund and an MMD Rate Lock provider pursuant to which the parties agree to make a net settlement payment to each other on a notional and duration amount, contingent upon whether the Municipal Market Data AAA General Obligation Scale is above or below a specified level on the expiration date of the contract. For example, if a Fund buys an MMD Rate Lock and the Municipal Market Data AAA General Obligation Scale is below the specified level on the expiration date, the counterparty to the contract will make a payment to a Fund equal to the specified level minus the actual level, multiplied by the notional amount of the contract. If the Municipal Market Data AAA General Obligation Scale is above the specified level on the expiration date, a Fund will make a payment to the counterparty equal to the actual level minus the specified level, multiplied by the notional amount of the contract. In connection with investments in MMD Rate Locks, there is a risk that municipal yields will move in the opposite direction than anticipated by a Fund, which would cause the Fund to make payments to its counterparty in the transaction that could adversely affect the Fund’s performance.
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| High Yield Investments Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | High-Yield Investments Risk. Securities and other debt instruments held by the Fund that are rated below investment grade (commonly called “high-yield” or “junk” bonds) and unrated debt instruments of comparable quality expose the Fund to a greater risk of loss of principal and income than a fund that invests solely or primarily in investment grade debt instruments. In addition, these investments have greater price fluctuations, are less liquid and are more likely to experience a default than higher-rated debt instruments. High-yield debt instruments are considered to be predominantly speculative with respect to the issuer’s capacity to pay interest and repay principal.
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| Impairment of Collateral Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Impairment of Collateral Risk. The value of collateral, if any, securing a loan can decline, and may be insufficient to meet the borrower’s obligations or difficult or costly to liquidate. In addition, the Fund’s access to collateral may be limited by bankruptcy or other insolvency laws. Further, certain floating rate and other loans may not be fully collateralized and may decline in value.
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| Interest Rate Risks [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Interest Rate Risk. Interest rate risk is the risk of losses attributable to changes in interest rates. In general, if interest rates rise, the values of debt instruments tend to fall, and if interest rates fall, the values of debt instruments tend to rise. Changes in the value of a debt instrument usually will not affect the amount of income the Fund receives from it but will generally affect the value of your investment in the Fund. Changes in interest rates may also affect the liquidity of the Fund’s investments in debt instruments. In general, the longer the maturity or duration of a debt instrument, the greater its sensitivity to changes in interest rates. For example, a three-year duration means a bond is expected to decrease in value by 3% if interest rates rise 1% and increase in value by 3% if interest rates fall 1%. Interest rate declines also may increase prepayments of debt obligations, which, in turn, would increase prepayment risk. The Fund is subject to the risk that the income generated by its investments may not keep pace with inflation. Actions by governments and central banking authorities can result in increases or decreases in interest rates. Higher periods of inflation could lead such authorities to raise interest rates. Such actions may negatively affect the value of debt instruments held by the Fund, resulting in a negative impact on the Fund's performance and NAV. Any interest rate increases could cause the value of the Fund’s investments in debt instruments to decrease. Rising interest rates may prompt redemptions from the Fund, which may force the Fund to sell investments at a time when it is not advantageous to do so, which could result in losses.
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| Leverage Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Leverage Risk. Leverage occurs when the Fund increases its assets available for investment using borrowings, derivatives or similar instruments or techniques. Use of leverage can produce volatility and may exaggerate changes in the NAV of Fund shares and in the return on the Fund’s portfolio, which may increase the risk that the Fund will lose more than it has invested. If the Fund uses leverage, through the purchase of particular instruments such as derivatives, the Fund may experience capital losses that exceed the net assets of the Fund. Leverage can create an interest expense that may lower the Fund's overall returns. Leverage presents the opportunity for increased net income and capital gains, but may also exaggerate the Fund’s volatility and risk of loss. There can be no guarantee that a leveraging strategy will be successful.
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| Liquidity Risk [Member] | |
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| Risk [Text Block] | Liquidity Risk. Liquidity risk is the risk associated with any event, circumstance, or characteristic of an investment or market that negatively impacts the Fund’s ability to sell, or realize the proceeds from the sale of, an investment at a desirable time or price. Liquidity risk may arise because of, for example, a lack of marketability of the investment, which means that when seeking to sell its portfolio investments, the Fund could find that selling is more difficult than anticipated, especially during times of high market volatility. Decreases in the number of financial institutions, including banks and broker-dealers, willing to make markets (match up sellers and buyers) in the Fund’s investments or decreases in their capacity or willingness to trade such investments may increase the Fund’s exposure to this risk. The debt market has experienced considerable growth, and financial institutions making markets in instruments purchased and sold by the Fund (e.g., bond dealers) have been subject to increased regulation. The impact of that growth and regulation on the ability and willingness of financial institutions to engage in trading or “making a market” in such instruments remains unsettled. Certain types of investments, such as lower-rated securities or those that are purchased and sold in over-the-counter markets, may be especially subject to liquidity risk. Securities or other assets in which the Fund invests may be traded in the over-the-counter market rather than on an exchange and therefore may be more difficult to purchase or sell at a fair price, which may have a negative impact on the Fund’s performance. Market participants attempting to sell the same or a similar instrument at the same time as the Fund could exacerbate the Fund’s exposure to liquidity risk. The Fund may have to accept a lower selling price for the holding, sell other liquid or more liquid investments that it might otherwise prefer to hold (thereby increasing the proportion of the Fund’s investments in less liquid or illiquid securities), or forego another more appealing investment opportunity. The liquidity of Fund investments may change significantly over time and certain investments that were liquid when purchased by the Fund may later become illiquid, particularly in times of overall economic distress. Changing regulatory, market or other conditions or environments (for example, the interest rate or credit environments) may also adversely affect the liquidity and the price of the Fund's investments. Judgment plays a larger role in valuing illiquid or less liquid investments as compared to valuing liquid or more liquid investments. Price volatility may be higher for illiquid or less liquid investments as a result of, for example, the relatively less frequent pricing of such securities (as compared to liquid or more liquid investments). Generally, the less liquid the market at the time the Fund sells a portfolio investment, the greater the risk of loss or decline of value to the Fund. Overall market liquidity and other factors can lead to an increase in redemptions, which may negatively impact Fund performance and NAV, including, for example, if the Fund is forced to sell investments in a down market. The municipal securities market is an over-the-counter market, which means that the Fund purchases and sells investments through municipal bond dealers. The Fund’s ability to sell investments held in its portfolio is dependent on the willingness and ability of market participants to provide bids that, in the view of portfolio management, reflect current market prices. Adverse market conditions could result in a lack of liquidity by reducing the number of ready buyers.
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| Market Risk [Member] | |
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| Risk [Text Block] | Market Risk. The Fund may incur losses due to declines in the value of one or more securities in which it invests. These declines may be due to factors affecting a particular issuer, or the result of, among other things, political, regulatory, market, economic or social developments affecting the relevant market(s) more generally. In addition, turbulence in financial markets and reduced liquidity in equity, credit and/or fixed income markets may negatively affect many issuers, which could adversely affect the Fund’s ability to price or value hard-to-value assets in thinly traded and closed markets and could cause significant redemptions and operational challenges. Global economies and financial markets are increasingly interconnected, and conditions and events in one country, region or financial market may adversely impact issuers in a different country, region or financial market. These risks may be magnified if certain events or developments adversely interrupt the global supply chain; in these and other circumstances, such risks might affect companies worldwide. As a result, local, regional or global events such as terrorism, war, other conflicts, natural disasters, disease/virus outbreaks and epidemics or other public health issues, recessions, depressions or other events – or the potential for such events – could have a significant negative impact on global economic and market conditions.
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| Municipal Securities Risk [Member] | |
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| Risk [Text Block] | Municipal Securities Risk. Municipal securities are debt obligations generally issued to obtain funds for various public purposes, including general financing for state and local governments, or financing for a specific project or public facility, and include obligations of the governments of the U.S. territories, commonwealths and possessions such as Guam, Puerto Rico and the U.S. Virgin Islands to the extent such obligations are exempt from state and U.S. federal income taxes. The value of municipal securities can be significantly affected by actual or expected political and legislative changes at the federal or state level. Municipal securities may be fully or partially backed by the taxing authority of the local government, by the credit of a private issuer, by the current or anticipated revenues from a specific project or specific assets or by domestic or foreign entities providing credit support, such as letters of credit, guarantees or insurance, and are generally classified into general obligation bonds and special revenue obligations. Because many municipal securities are issued to finance projects in sectors such as education, health care, transportation and utilities, conditions in those sectors can affect the overall municipal market. Issuers in a state, territory, commonwealth or possession in which the Fund invests may experience significant financial difficulties for various reasons, including as the result of events that cannot be reasonably anticipated or controlled such as economic downturns or similar periods of economic stress, social conflict or unrest, labor disruption and natural disasters. Such financial difficulties may lead to credit rating downgrades or defaults of such issuers which in turn, could affect the market values and marketability of many or all municipal obligations of issuers in such state, territory, commonwealth or possession. The value of the Fund’s shares will be negatively impacted to the extent it invests in such securities. The Fund’s Form N-CSR shows the Fund’s investment exposures at a point in time. The risk of investing in the Fund is directly correlated to the Fund’s investment exposures. Because the Fund invests substantially in municipal securities issued by the state identified in the Fund’s name and political sub-divisions of that state, the Fund will be particularly affected by adverse tax, legislative, regulatory, demographic or political changes as well as changes impacting the state's financial, economic or other condition and prospects. In addition, because of the relatively small number of issuers of tax-exempt securities in the state, the Fund may invest a higher percentage of assets in a single issuer and, therefore, be more exposed to the risk of loss than a fund that invests more broadly. The value of municipal and other securities owned by the Fund also may be adversely affected by future changes in federal or state income tax laws.
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| Prepayment and Extension Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Prepayment and Extension Risk. Prepayment and extension risk is the risk that a bond or other security or investment might, in the case of prepayment risk, be called or otherwise converted, prepaid or redeemed before maturity and, in the case of extension risk, that the investment might not be called as expected. In the case of prepayment risk, if the investment is converted, prepaid or redeemed before maturity, the portfolio managers may not be able to invest the proceeds in other investments providing as high a level of income, resulting in a reduced yield to the Fund. As interest rates decrease or spreads narrow on such investments, the likelihood of prepayment increases. Conversely, extension risk is the risk that an unexpected rise in interest rates will extend the life of an investment beyond the prepayment time. If the Fund’s investments are locked in at a lower interest rate for a longer period of time, the portfolio managers may be unable to capitalize on investments with higher interest rates or wider spreads.
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| Reinvestment Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Reinvestment Risk. Reinvestment risk arises when the Fund is unable to reinvest income or principal at the same or at least the same return it is currently earning.
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| Tax Risk [Member] | |
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| Risk [Text Block] | Tax Risk. Municipal securities generally pay interest that, in the opinion of bond counsel, is free from U.S. federal income tax (and in most cases, the U.S. federal alternative minimum tax). A portion of the Fund’s income from such bonds may be taxable to shareholders subject to the U.S. federal alternative minimum tax. Income from tax-exempt municipal obligations could be declared taxable, possibly retroactively, because of unfavorable changes in tax laws, adverse interpretations by the Internal Revenue Service, the non-compliant conduct of a bond issuer or under other circumstances. In such event, then the value of the security would likely fall and, as a shareholder of the Fund, you may be required to file an amended tax return and pay additional taxes.
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| Tender Option Bond Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Tender Option Bond Risk. TOB transactions expose the Fund to leverage and credit risk, and generally involve greater risk than direct investments in fixed rate municipal bonds, including the risk of loss of principal. The interest payments that the Fund would typically receive in connection with a TOB transaction (inverse floaters) vary inversely with short-term interest rates and will be reduced (and potentially eliminated) when short-term interest rates increase. In addition, the Fund will be subject to leverage risk to the extent that the Fund uses the proceeds that it receives from a TOB transaction to invest in other securities. The Fund’s investment in a TOB will generally underperform the market for fixed rate municipal securities when interest rates rise. The value of and market for such inverse floaters can be volatile and can have limited liquidity. Investments in inverse floaters issued in TOB transactions are derivative instruments and, therefore, are also subject to the risks generally applicable to investments in derivatives.
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| Active Management Risk [Member] | |
| Prospectus [Line Items] | |
| Risk [Text Block] | Active Management Risk. Due to its active management, the Fund could underperform its benchmark index and/or other funds with similar investment objectives and/or strategies.
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| Risk Lose Money [Member] | |
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| Risk [Text Block] | There is no assurance that the Fund will achieve its investment objective and you may lose money. |
| Risk Not Insured Depository Institution [Member] | |
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| Risk [Text Block] | An investment in the Fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. |