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MainStay Short Term Bond Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MainStay Short Term Bond Fund (formerly known as MainStay Indexed Bond Fund)
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks current income consistent with capital preservation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may be required to pay a commission or other transaction charge to your financial intermediary for effecting transactions in a class of shares of the Fund that has no initial sales charge, contingent deferred sales charge, or other asset-based fee for sales or distribution, such as Class I or Class R6 shares. These commissions are not reflected in the fee and expense table or expense example below. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the MainStay Funds. This amount may vary depending on the MainStay Fund in which you invest. In addition, different financial intermediary firms and financial professionals may impose different sales loads and waivers. More information about these and other discounts or waivers is available from your financial professional, in the "Information on Sales Charges" section starting on page 130 of the Prospectus and Appendix A – Intermediary-Specific Sales Charge Waivers and Discounts, and in the "Alternative Sales Arrangements" section on page 123 of the Statement of Additional Information.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination Feb. 28, 2021
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the Example, affect the Fund's performance. During the most recent fiscal year, the Fund's portfolio turnover rate was 75% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 75.00%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in the MainStay Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

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. 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:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund, under normal circumstances, invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in debt securities.


Under normal circumstances, the Fund invests at least 80% of net assets in investment grade quality bonds of various types as rated by a nationally recognized statistical rating organization (“NRSRO”) (such bonds rated BBB- or higher, or Baa3 or higher), or if unrated, judged to be of comparable quality by NYL Investors LLC, the Fund’s Subadvisor. The Fund may invest up to 20% of its net assets in bonds rated below investment grade by a NRSRO (such as bonds rated lower than BBB- and Baa3), commonly referred to as “high yield” or “junk” bonds.


The Fund's principal investments include investment grade corporate credit and securitized assets, including structured credit, collateralized loan obligations, asset-backed securities, residential mortgage-backed securities, commercial mortgage-backed securities and collateralized mortgage obligations.


The Fund attempts to manage interest rate risk through its management of the average duration of the securities it holds in its portfolio. Under normal conditions, the Fund will maintain its average dollar-weighted duration range between one and three years. Duration is a measure used to determine the sensitivity of a security's price to changes in interest rates. The longer a security's duration, the more sensitive it will be to changes in interest rates.


The Fund may also invest in futures to seek to enhance returns or reduce the risk of loss by hedging certain of its holdings.


Investment Process: The Subadvisor seeks to generate consistent, risk-adjusted excess returns by conducting bottom-up fundamental research as the basis for investment selection.


Core to the Subadvisor’s objective is capital preservation through loss-avoidance by constructing a well-diversified portfolio with a long-term focus. Underlying investment opportunities are based on the financial condition and competitiveness of individual companies. The Subadvisor also invests in companies that the Subadvisor believes have a high margin of safety and are leaders in industries with high barriers to entry.


The Subadvisor prefers companies with positive free cash flow, solid asset coverage and management teams with strong track records. In virtually every phase of the investment process, the Subadvisor attempts to control risk and limit defaults.


The Subadvisor may sell a security if it believes the security will no longer contribute to meeting the investment objective of the Fund.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

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.


Net Asset Value Risk: The Fund is not a money market fund, does not attempt to maintain a stable net asset value, and is not subject to the rules that govern the quality, maturity, liquidity and other features of securities that money market funds may purchase. Under normal conditions, the Fund’s investments may be more susceptible than those of a money market fund to interest rate risk, valuation risk, credit risk and other risks relevant to the Fund’s investments. The Fund’s net asset value per share will fluctuate.


Market Risk: The value of the Fund’s investments may fluctuate because of changes in the markets in which the Fund invests, which could cause the Fund to underperform other funds with similar investment objectives and strategies. Such changes may be rapid and unpredictable. From time to time, markets may experience periods of stress for potentially prolonged periods that may result in: (i) increased market volatility; (ii) reduced market liquidity; and (iii) increased redemptions of Fund shares. Such conditions may add significantly to the risk of volatility in the net asset value of the Fund's shares.


Portfolio Management Risk: The investment strategies, practices and risk analyses used by the Subadvisor may not produce the desired results. In addition, the Fund may not achieve its investment objective, including during periods in which the Subadvisor takes temporary positions in response to unusual or adverse market, economic or political conditions, or other unusual or abnormal circumstances.


Yield Risk: There can be no guarantee that the Fund will achieve or maintain any particular level of yield.


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 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 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 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).


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.


High-Yield Securities Risk: Investments in high-yield securities or non-investment grade securities (commonly referred to as "junk bonds") are considered speculative because investments in such securities present a greater risk of loss than investments in higher quality securities. Such securities may, under certain circumstances, be less liquid than higher rated securities. These securities pay investors a premium (a high interest rate or yield) because of the potential illiquidity and increased risk of loss. These securities can also be subject to greater price volatility. In times of unusual or adverse market, economic or political conditions, these securities may experience higher than normal default rates.


Mortgage Pass-Through Securities Risk: Investments in mortgage pass-through securities are subject to similar market risks as fixed-income securities, which include, but are not limited to, interest rate risk, credit risk, prepayment risk, and extension risk.


Floating Rate Notes and Variable Rate Notes Risk: Floating and variable rate notes provide for a periodic adjustment in the interest rate paid on the securities. The rate adjustment intervals may be regular and range from daily up to annually, or may be based on an event, such as a change in the prime rate. Floating and variable rate notes may be subject to greater liquidity risk than other debt securities, meaning that there may be limitations on the Fund's ability to sell the securities at any given time. Securities with floating interest rates generally are less sensitive to interest rate changes, but may decline in value if their interest rates do not rise as much or as fast as interest rates in general. The terms of many floating rate notes and other instruments are tied to the London Interbank Offered Rate (“LIBOR”), which functions as a reference rate or benchmark. It is anticipated that LIBOR will be discontinued at the end of 2021, which may cause increased volatility and illiquidity in the markets for instruments with terms tied to LIBOR or other adverse consequences for these instruments. These events may adversely affect the Fund and its investments in such instruments.


Mortgage-Related and Other Asset-Backed Securities Risk: Investments in mortgage-related securities (such as mortgage-backed securities) and other asset-backed securities generally involve a stream of payments based on the underlying obligations. These payments, which are often part interest and part return of principal, vary based on the rate at which the underlying borrowers repay their loans or other obligations. Asset-backed securities are subject to the risk that borrowers may default on the underlying obligations and that, during periods of falling interest rates, these obligations may be called or prepaid and, during periods of rising interest rates, obligations may be paid more slowly than expected. Impairment of the underlying obligations or collateral, such as by non-payment, will reduce the security's value. Enforcing rights against such collateral in events of default may be difficult or insufficient. The value of these securities may be significantly affected by changes in interest rates, the market's perception of issuers, and the creditworthiness of the parties involved. These securities may have a structure that makes their reaction to interest rate changes and other factors difficult to predict, making their value highly volatile.


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 expose the Fund to greater risk than if it had invested 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. Derivatives may be difficult to sell, unwind 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 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 asset, the Fund may not be able to profitably exercise an option and may lose its entire investment in an option. Derivatives may also increase the expenses of the Fund.


Liquidity and Valuation Risk: The Fund’s investments may be illiquid at the time of purchase or liquid at the time of purchase and subsequently become illiquid due to, among other things, events relating to the issuer of the securities, market events, operational issues, economic conditions, investor perceptions or lack of market participants. The lack of an active trading market may make it difficult to sell or obtain an accurate price for a security. If market conditions or issuer specific developments make it difficult to value securities, the Fund may value these securities using more subjective methods, such as fair value pricing. In such cases, the value determined for a security could be different than the value realized upon such security's sale. As a result, an investor could pay more than the market value when buying Fund shares or receive less than the market value when selling Fund shares. This could affect the proceeds of any redemption or the number of shares an investor receives upon purchase.


The Fund is subject to the risk that it could not meet redemption requests within the allowable time period without significant dilution of remaining investors' interests in the Fund. To meet redemption requests or to raise cash to pursue other investment opportunities, the Fund may be forced to sell securities at an unfavorable time and/or under unfavorable conditions, which may adversely affect the Fund.


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 Lose Money [Text] rr_RiskLoseMoney You can lose money by investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured 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.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following bar chart and table indicate some of the risks of investing in the Fund. The bar chart shows you how the Fund's calendar year performance has varied over time. Sales loads, if any, are not reflected in the bar chart. If they were, returns would be less than those shown. The average annual total returns table shows how the Fund's average annual total returns (before and after taxes) compare to those of a broad-based securities market index. The Fund has selected the Bloomberg Barclays 1-3 Year U.S. Government/Credit Bond Index as its primary benchmark as a replacement for the Bloomberg Barclays U.S. Aggregate Bond Index because it believes that the Bloomberg Barclays 1-3 Year U.S. Government/Credit Bond Index is more reflective of its current investment style. The Bloomberg Barclays 1-3 Year U.S. Government/Credit Bond Index is an unmanaged index comprised of investment grade, U.S. dollar-denominated, fixed-rate Treasuries, government-related and corporate securities, with maturities of one to three years. The Bloomberg Barclays U.S. Aggregate Bond Index is a broad-based benchmark that measures the investment grade, U.S. dollar-denominated, fixed-rate taxable bond market, including Treasuries, government-related and corporate securities, mortgage-backed securities (agency fixed-rate and hybrid adjustable rate mortgage pass-throughs), asset-backed securities, and commercial mortgage-backed securities.


Performance data for the classes varies based on differences in their fee and expense structures. Performance data is not shown for classes with less than one calendar year of performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Please visit nylinvestments.com/funds for more recent performance information.


Effective December 5, 2019, the Fund's investment objective and principal investment strategies changed. Prior to that date, the Fund operated as an index fund and sought to match the return of its former benchmark gross of fees. The past performance in the bar chart and table prior to that date reflects the Fund’s prior investment objective and principal investment strategies.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following bar chart and table indicate some of the risks of investing in the Fund.
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Performance data is not shown for classes with less than one calendar year of performance.
Performance Additional Market Index [Text] rr_PerformanceAdditionalMarketIndex The Bloomberg Barclays U.S. Aggregate Bond Index is a broad-based benchmark that measures the investment grade, U.S. dollar-denominated, fixed-rate taxable bond market, including Treasuries, government-related and corporate securities, mortgage-backed securities (agency fixed-rate and hybrid adjustable rate mortgage pass-throughs), asset-backed securities, and commercial mortgage-backed securities.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress nylinvestments.com/funds
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Returns, Class I Shares (by calendar year 2010-2019)
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads Sales loads, if any, are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
   

Best Quarter

 

2Q/10

3.60

%

Worst Quarter

 

4Q/16

-3.12

%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.60%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.12%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2019)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged The Fund has selected the Bloomberg Barclays 1-3 Year U.S. Government/Credit Bond Index as its primary benchmark as a replacement for the Bloomberg Barclays U.S. Aggregate Bond Index because it believes that the Bloomberg Barclays 1-3 Year U.S. Government/Credit Bond Index is more reflective of its current investment style.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deductions for fees, expenses, or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest individual federal marginal income tax rates in effect at the time of each distribution or capital gain or upon the sale of Fund shares, and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred 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 One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns shown are for Class I shares. After-tax returns for the other share classes may vary.
Performance Table Explanation after Tax Higher rr_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.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest individual federal marginal income tax rates in effect at the time of each distribution or capital gain or upon the sale of Fund shares, and do not reflect the impact of state and local taxes. 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. 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. After-tax returns shown are for Class I shares. After-tax returns for the other share classes may vary.
MainStay Short Term Bond Fund | Bloomberg Barclays 1-3 Year U.S. Government/Credit Bond Index (reflects no deductions for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 4.03%
5 Years rr_AverageAnnualReturnYear05 1.67%
10 Years rr_AverageAnnualReturnYear10 1.54%
MainStay Short Term Bond Fund | Bloomberg Barclays U.S. Aggregate Bond Index (reflects no deductions for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 8.72%
5 Years rr_AverageAnnualReturnYear05 3.05%
10 Years rr_AverageAnnualReturnYear10 3.75%
MainStay Short Term Bond Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 1.00%
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none [1]
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.25% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.24% [3]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.74%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets none [4]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 0.74% [4]
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock No initial sales charge applies on investments of $250,000 or more (and certain other qualified purchases). However, a contingent deferred sales charge of 0.50% may be imposed on certain redemptions made within 12 months of the date of purchase on shares that were purchased without an initial sales charge.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 175
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 334
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 507
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,009
1 Year rr_AverageAnnualReturnYear01 4.98%
5 Years rr_AverageAnnualReturnYear05 1.73%
10 Years rr_AverageAnnualReturnYear10 2.68%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 02, 2004
MainStay Short Term Bond Fund | Investor Class  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 1.00%
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none [1]
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.25% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.72% [3]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.22%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.30%) [4]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 0.92% [4]
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock No initial sales charge applies on investments of $250,000 or more (and certain other qualified purchases). However, a contingent deferred sales charge of 0.50% may be imposed on certain redemptions made within 12 months of the date of purchase on shares that were purchased without an initial sales charge.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 193
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 454
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 735
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,536
1 Year rr_AverageAnnualReturnYear01 4.62%
5 Years rr_AverageAnnualReturnYear05 1.48%
10 Years rr_AverageAnnualReturnYear10 2.49%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 28, 2008
MainStay Short Term Bond Fund | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.25% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.24% [3]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.49%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.09%) [4]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 0.40% [4]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 41
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 148
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 265
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 607
Annual Return 2010 rr_AnnualReturn2010 6.00%
Annual Return 2011 rr_AnnualReturn2011 7.22%
Annual Return 2012 rr_AnnualReturn2012 3.84%
Annual Return 2013 rr_AnnualReturn2013 (2.43%)
Annual Return 2014 rr_AnnualReturn2014 5.75%
Annual Return 2015 rr_AnnualReturn2015 0.16%
Annual Return 2016 rr_AnnualReturn2016 2.16%
Annual Return 2017 rr_AnnualReturn2017 3.19%
Annual Return 2018 rr_AnnualReturn2018 (0.57%)
Annual Return 2019 rr_AnnualReturn2019 8.49%
1 Year rr_AverageAnnualReturnYear01 8.49%
5 Years rr_AverageAnnualReturnYear05 2.64%
10 Years rr_AverageAnnualReturnYear10 3.32%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 02, 1991
MainStay Short Term Bond Fund | Class I | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 6.50%
5 Years rr_AverageAnnualReturnYear05 1.23%
10 Years rr_AverageAnnualReturnYear10 1.94%
MainStay Short Term Bond Fund | Class I | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 5.11%
5 Years rr_AverageAnnualReturnYear05 1.43%
10 Years rr_AverageAnnualReturnYear10 2.06%
MainStay Short Term Bond Fund | Class R6  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of the lesser of the original offering price or redemption proceeds) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.25% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.20% [3]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.45%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.05%) [4]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 0.40% [4]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 41
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 139
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 247
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 562
[1] No initial sales charge applies on investments of $250,000 or more (and certain other qualified purchases). However, a contingent deferred sales charge of 0.50% may be imposed on certain redemptions made within 12 months of the date of purchase on shares that were purchased without an initial sales charge.
[2] The management fee is as follows: 0.25% on assets up to $1 billion; and 0.20% on assets over $1 billion.
[3] Restated to reflect the expenses expected to be incurred during the current fiscal year.
[4] New York Life Investment Management LLC ("New York Life Investments") has contractually agreed to waive fees and/or reimburse expenses so that Total Annual Fund Operating Expenses (excluding taxes, interest, litigation, extraordinary expenses, brokerage and other transaction expenses relating to the purchase or sale of portfolio investments, and acquired (underlying) fund fees and expenses) do not exceed the following percentages of its average daily net assets: Class A, 0.82%; Investor Class, 0.92%; and Class I, 0.40%. In addition, New York Life Investments will waive fees and/or reimburse expenses so that Total Annual Fund Operating Expenses (excluding taxes, interest, litigation, extraordinary expenses, brokerage and other transaction expenses relating to the purchase or sale of portfolio investments, and acquired (underlying) fund fees and expenses) of Class R6 do not exceed those of Class I. This agreement will remain in effect until February 28, 2021, and shall renew automatically for one-year terms unless New York Life Investments provides written notice of termination prior to the start of the next term or upon approval of the Board of Trustees of the Fund.