The Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated whether or not you redeem all of your shares at the end of those periods (except as indicated with respect to Class C and Class C2 shares). The Example reflects Class C and Class C2 shares converting into Investor Class shares in years 9-10; expenses could be lower if you are eligible to convert to Class A shares instead. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. The Example reflects the contractual fee waiver and/or expense reimbursement arrangement, if applicable, for the current duration of the arrangement only. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Expense Example, No Redemption, By Year, Caption [Text]

oef_ExpenseExampleNoRedemptionByYearCaption

Assuming no redemption

Strategy Narrative [Text Block]

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The Fund, under normal circumstances, invests at least 80% of its assets (net assets plus borrowings for investment purposes) in municipal bonds that are rated investment grade by at least one nationally recognized statistical rating organization (“NRSRO”). Municipal bonds are issued to raise money for a variety of public and private purposes, including general financing for state and local governments, financing for eligible non-profit organizations, or financing for a specific project or public facility. Municipal securities usually pay a fixed, variable, or floating rate of interest, and must repay the amount borrowed, usually at the maturity of the security. On average, the Fund will invest in municipal bonds that have a maturity range of 10 to 30 years. Municipal bonds are issued by or on behalf of the District of Columbia, states, territories, commonwealths and possessions of the United States and their political subdivisions and agencies, authorities and instrumentalities. Municipal bonds include, among other instruments, general obligation bonds, revenue bonds, industrial revenue bonds, industrial development bonds, private activity bonds, as well as short-term, tax-exempt obligations such as municipal notes and variable rate demand obligations. The Fund may invest up to 20% of its net assets in unrated securities deemed by MacKay Shields LLC, the Fund's Subadvisor, to be of comparable quality. The Fund may not invest more than 20% of its net assets in tax-exempt securities subject to the federal alternative minimum tax. If NRSROs assign different ratings to the same security, the Fund will use the higher rating for purposes of determining the security’s credit quality.

The Fund may invest more than 25% of its total assets in municipal bonds that are related in such a way that an economic, business or political development or change affecting one such security could also affect the other securities (for example, securities whose issuers are located in the same state). Some of the Fund's earnings may be subject to federal tax and most may be subject to state and local taxes.

The Fund may invest in derivatives, such as futures, options and swap agreements to seek enhanced returns or to reduce the risk of loss by hedging certain of its holdings.

Investment Process: The Subadvisor employs a relative value research-driven approach in pursuing the Fund's investment objective. The Subadvisor's strategies include duration management, sector allocation, yield curve positioning and buy/sell trade execution. The Subadvisor may engage in various portfolio strategies to achieve the Fund's investment objective, to seek to enhance the Fund's investment return and to seek to hedge the portfolio against adverse effects from movements in interest rates and in the securities markets.

The Subadvisor uses active management in an effort to identify mispriced tax-exempt securities and build a consistent yield advantage. The Subadvisor focuses on reducing volatility through a disciplined investment process which includes fundamental, "bottom-up" credit research and risk management. In addition, the Subadvisor reviews macroeconomic events, technicals in the municipal market, tax policies and analyzes individual municipal securities and sectors. The Subadvisor’s investment process includes a risk analysis that gives consideration to a variety of security-specific risks, including but not limited to, environmental, social and governance (“ESG”) risks that may have a material impact on the performance of a security. In addition to proprietary research, the Subadvisor may use screening tools and, to the extent available, third party data to identify ESG risk factors that may not have been captured through its own research. The Subadvisor’s consideration of ESG risk is weighed against other criteria and no sectors or industries are explicitly excluded from the Fund.

The Subadvisor may sell a security if it no longer believes the security will contribute to meeting the investment objective of the Fund. In considering whether to sell a security, the Subadvisor may evaluate, among other things, the condition of the economy and meaningful changes in the issuer's financial condition.

Bar Chart and Performance Table [Heading]

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Past Performance

Performance One Year or Less [Text]

oef_PerformanceOneYearOrLess

Performance data is not shown for classes with less than one calendar year of performance.

Performance Past Does Not Indicate Future [Text]

oef_PerformancePastDoesNotIndicateFuture

Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Bar Chart Does Not Reflect Sales Loads [Text]

oef_BarChartDoesNotReflectSalesLoads

Sales loads, if any, are not reflected in the bar chart. If they were, returns would be less than those shown.

Performance Table Heading

oef_PerformanceTableHeading

Average Annual Total Returns (for the periods ended December 31, 2025)

Performance Table Not Relevant to Tax Deferred

oef_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your tax situation and may differ from those shown. After-tax returns are not relevant if you hold your shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Performance Table Explanation after Tax Higher

oef_PerformanceTableExplanationAfterTaxHigher

In some cases, the return after taxes may exceed the return before taxes due to an assumed tax benefit from any losses on a sale of shares at the end of the measurement period.

Risk [Text Block]

oef_RiskTextBlock

Principal Risks

You can lose money by investing in the Fund. 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 governmental agency. The investments selected by the Subadvisor may underperform the market in which the Fund invests or other investments. The Fund may receive large purchase or redemption orders which may have adverse effects on performance if the Fund were required to sell securities, invest cash or hold a relatively large amount of cash at times when it would not otherwise do so.

The principal risks of investing in the Fund are summarized below. The relative significance of each principal risk summarized below may change over time.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

oef_RiskTextBlock

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 governmental agency.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

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Portfolio Management Risk: The investment strategies, practices and risk analyses used by the Subadvisor may not produce the desired results or expected returns. The Subadvisor may give consideration to certain ESG criteria when evaluating an investment opportunity. The application of ESG criteria may result in the Fund (i) having exposure to certain securities or industry sectors that are different than the composition of the Fund's benchmark; and (ii) performing differently than other funds and strategies in its peer group that do not take into account ESG criteria or the Fund's benchmark.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

oef_RiskTextBlock

Debt Securities Risk: The risks of investing in debt or fixed-income securities include (without limitation): (i) credit risk, e.g., the issuer or guarantor of a debt security may be unable or unwilling (or be perceived by market participants, rating agencies, pricing services or otherwise as unable or unwilling) to make timely principal and/or interest payments or otherwise honor its obligations, or changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may affect the value of the Fund’s investments; (ii) maturity risk, e.g., a debt security with a longer maturity may fluctuate in value more than one with a shorter maturity; (iii) market risk, e.g., low demand for debt securities may negatively impact their price; (iv) interest rate risk, e.g., when interest rates go up, the value of a debt security generally goes down, and when interest rates go down, the value of a debt security generally goes up (long-term debt securities are generally more susceptible to interest rate risk than short-term debt securities); and (v) call or prepayment risk, e.g., during a period of falling interest rates, the issuer may redeem a security by repaying it early, which may reduce the Fund’s income if the proceeds are reinvested at lower interest rates.

Interest rate risk is the risk that the value of the Fund’s investments in fixed-income or debt securities will change because of changes in interest rates. There is a risk that interest rates across the financial system may change, possibly significantly and/or rapidly. Changes in interest rates (or the expectation of such changes) or a lack of market participants may lead to decreased liquidity and increased volatility in the fixed-income or debt markets, making it more difficult for the Fund to sell its fixed-income or debt holdings. Decreased liquidity in the fixed-income or debt markets also may make it more difficult to value some or all of the Fund’s fixed-income or debt holdings. For most fixed-income investments, when market interest rates fall, prices of previously-issued fixed-rate debt securities rise. However, when market interest rates fall, prices of certain variable and fixed-rate debt securities may be adversely affected (i.e., falling interest rates bring the possibility of prepayment risk, as an instrument may be redeemed before maturity). Very low or negative interest rates may magnify interest rate risk. There is a risk that the income generated by investments may not keep pace with inflation. Actions by governments and central banking authorities can result in increases or decreases in interest rates. Periods of higher inflation could cause such authorities to raise interest rates, which may adversely affect the Fund and its investments. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, may result in heightened market volatility and may detract from Fund performance to the extent the Fund is exposed to such interest rates and/or volatility. Other factors that may affect the value of debt securities include, but are not limited to, economic, social, political, public health, and other crises and responses by governments and companies to such crises.

Not all U.S. government debt securities are guaranteed by the U.S. government—some are backed only by the issuing agency, which must rely on its own resources to repay the debt. The Fund's yield will fluctuate with changes in short-term interest rates.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

oef_RiskTextBlock

Derivatives Risk: Derivatives are investments whose value depends on (or is derived from) the value of an underlying instrument, such as a security, asset, reference rate or index. Derivative strategies may be riskier than investing directly in the underlying instrument and often involve leverage, which may exaggerate a loss, potentially causing the Fund to lose more money than it originally invested and would have lost had it invested directly in the underlying instrument. For example, if the Fund is the seller of credit protection in a credit default swap, the Fund effectively adds leverage to its portfolio and is subject to the credit exposure on the full notional value of the swap. Derivatives may be difficult to sell, unwind and/or value. Derivatives may also be subject to counterparty risk, which is the risk that the counterparty (the party on the other side of the transaction) on a derivative transaction will be unable or unwilling to honor its contractual obligations to the Fund. Futures and other derivatives may be more volatile than direct investments in the instrument underlying the contract, and may not correlate perfectly to the underlying instrument. Futures and other derivatives also may involve a small initial investment relative to the risk assumed, which could result in losses greater than if they had not been used. Due to fluctuations in the price of the underlying instrument, the Fund may not be able to profitably exercise an option and may lose its entire investment in an option. To the extent that the Fund writes or sells an option, if the decline in the value of the underlying instrument is significantly below the exercise price in the case of a written put option or increase above the exercise price in the case of a written call option, the Fund could experience a substantial loss. Swaps may be subject to counterparty credit, correlation, valuation, liquidity and leveraging risks. Swap transactions tend to shift a Fund's investment exposure from one type of investment to another and may entail the risk that a party will default on its payment obligations to the Fund. Additionally, applicable regulators have adopted rules imposing certain margin requirements, including minimums on uncleared swaps, which may result in the Fund and its counterparties posting higher margin amounts for uncleared swaps. Certain standardized swaps are subject to mandatory central clearing and exchange trading. Central clearing, which interposes a central clearinghouse to each participant’s swap, and exchange trading are intended to reduce counterparty credit risk and increase liquidity but neither makes swap transactions risk-free. Derivatives may also increase the expenses of the Fund.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

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Municipal Bond Focus Risk: From time to time the Fund may invest a substantial amount of its assets in municipal bonds on which interest is paid solely from revenues of similar projects. If the Fund focuses its investments in this manner, it assumes the legal and economic risks relating to such projects, which may have a significant impact on the Fund’s investment performance. In addition, the Fund may invest more heavily in bonds from certain cities, states or regions than others, which may increase the Fund’s exposure to losses resulting from economic, political or regulatory occurrences impacting these particular cities, states or regions.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

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Money Market/Short-Term Securities Risk: To the extent the Fund holds cash or invests in money market or short-term securities, the Fund may be less likely to achieve its investment objective. In addition, it is possible that the Fund's investments in these instruments could lose money.

Risk/Return:

oef_RiskReturnAbstract

Risk [Text Block]

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Private Placement and Restricted Securities Risk: The Fund may invest in privately issued securities, including those which may be resold only in accordance with Rule 144A under the Securities Act of 1933, as amended. Securities acquired in a private placement generally are subject to strict restrictions on resale, and there may be no market or a limited market for the resale of such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so or at the most favorable price. This potential lack of liquidity also may make it more difficult to accurately value these securities.

Risk/Return:

oef_RiskReturnAbstract

Average Annual Return, Percent

oef_AvgAnnlRtrPct

4.25%

Average Annual Return, Percent

oef_AvgAnnlRtrPct

2.34%

Risk/Return:

oef_RiskReturnAbstract

Maximum Deferred Sales Charge (as a percentage)

oef_MaximumDeferredSalesChargeOverOther

0.00%

^[2]

Distribution and Service (12b-1) Fees

oef_DistributionAndService12b1FeesOverAssets

0.25%

Expenses (as a percentage of Assets)

oef_ExpensesOverAssets

0.74%

Expense Example, with Redemption, 1 Year

oef_ExpenseExampleYear01

$ 373

Expense Example, with Redemption, 5 Years

oef_ExpenseExampleYear05

699

Average Annual Return, Percent

oef_AvgAnnlRtrPct

0.81%

Average Annual Return, Percent

oef_AvgAnnlRtrPct

1.86%

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

oef_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

2.50%

Management Fees (as a percentage of Assets)

oef_ManagementFeesOverAssets

0.41%

^[3]

Other Expenses (as a percentage of Assets):

oef_OtherExpensesOverAssets

0.12%

Expenses Deferred Charges [Text Block]

oef_ExpensesDeferredChargesTextBlock

No initial sales charge applies on investments of $250,000 or more (and certain other qualified purchases referenced within “Information on Sales Charges” in the Shareholder Guide). However, a contingent deferred sales charge of 1.00% may be imposed on certain redemptions made within 18 months of the date of purchase on shares that were purchased without an initial sales charge. For more information on contingent deferred sales charges, see “Sales Charges” in the Shareholder Guide.

Expense Example, with Redemption, 3 Years

oef_ExpenseExampleYear03

493

Expense Example, with Redemption, 10 Years

oef_ExpenseExampleYear10

$ 1,192

Average Annual Return, Percent

oef_AvgAnnlRtrPct

(0.40%)

Performance Inception Date

oef_PerfInceptionDate

Feb. 28, 2008