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Prospectus Summary | MainStay MacKay International Equity Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MainStay MacKay International Equity Fund
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term growth of capital.
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, hold and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and 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 70 of the Prospectus and Appendix A – Intermediary-Specific Sales Charge Waivers and Discounts, and in the "Alternative Sales Arrangements" section on page 142 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)
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 101% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 101.00%
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 (except as indicated with respect to Class B and Class C shares). The Example reflects Class B and Class C 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 by, Year, Caption [Text] rr_ExpenseExampleByYearCaption Assuming redemption at end of period
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption Assuming no redemption
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund invests in those companies that meet the quality and valuation criteria of MacKay Shields LLC, the Fund’s Subadvisor.

The Fund normally invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in equity securities of foreign issuers. Generally, an issuer is considered to be U.S. or foreign based on the issuer’s “country of risk,” as determined by a third-party service provider such as Bloomberg. The Fund invests in securities of companies which conduct business in a variety of countries, with a minimum of five countries other than the United States. This includes countries with established economies as well as emerging market countries that the Subadvisor believes present favorable opportunities. The Fund may also invest in exchange-traded funds ("ETFs") to obtain this exposure or for other investment purposes.

Investment Process: The Subadvisor seeks to identify investment opportunities through “bottom-up” analysis and fundamental research. The Subadvisor performs research to identify reasonably priced companies with competitive market advantages that it believes are able to benefit from long-term market trends and that the Subadvisor believes are able to sustain earnings growth over long periods of time, regardless of economic climate. The Subadvisor employs a two-stage process which begins by identifying companies using the following investment selection criteria:

· Secular Growth Dynamics

· Competitive Positioning

· Management Quality

· Economic Sensitivity

· Concentration Risk

· Financial Leverage

· Corporate Governance

Only companies that meet the Subadvisor’s requirements for each of the investment selection criteria are considered for inclusion in the Fund. The second step in the process combines the Subadvisor’s qualitative analysis with detailed financial analysis in order to rank the return potential of each investment opportunity. These rankings determine holdings and position sizing of equity securities in the Fund.

The Subadvisor also believes that environmental, social and governance (“ESG”) factors contribute to long-term market trends and actively considers these factors in its investment process. The Subadvisor’s ESG analysis includes its own proprietary assessments of ESG factors. 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 therefore does not mean that any sectors or industries are explicitly excluded from the Fund.

Allocations to countries and industries are also a result of the "bottom-up" stock selection process and, as a result, may deviate from the country and industry weightings in the Fund’s benchmark. The Fund may not perform as well as its peers or benchmark during periods when the stock market favors the securities of businesses with lower operating margins, more highly leveraged balance sheets, or more economic sensitivity.

Generally, the Fund seeks to limit its investments in securities of: (i) any one company; (ii) companies in the same industry; (iii) companies located in any one country; and (iv) companies located in emerging markets (currently limited to 25% of the Fund’s assets measured at the time of investment).

The Subadvisor may sell a security if it believes the security will no longer contribute to meeting the investment objective of the Fund. In considering whether to sell a security, the Subadvisor may evaluate, among other things, whether the security has approached full valuation, if the investment thesis is invalidated, if superior opportunities to redeploy exist or emerge, or if industry group or country weights or individual positions need to be adjusted.
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.

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. 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 significantly 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.

Equity Securities Risk: Investments in common stocks and other equity securities are particularly subject to the risk of changing economic, stock market, industry and company conditions and the risks inherent in the portfolio managers' ability to anticipate such changes that can adversely affect the value of the Fund's holdings.

Focused Portfolio Risk: Because the Fund typically invests in relatively few holdings, a larger percentage of its assets may be invested in a particular issuer or in fewer companies than is typical of other mutual funds. This may increase volatility of the Fund’s NAVs. The Fund will be more susceptible to adverse economic, political, regulatory or market developments affecting a single issuer than a fund that is invested more broadly.

Foreign Securities Risk: Investments in foreign (non-U.S.) securities may be riskier than investments in U.S. securities. Foreign regulatory regimes and securities markets can have less stringent investor protections and disclosure standards and less liquid trading markets than U.S. regulatory regimes and securities markets, and can experience political, social and economic developments that may affect the value of the Fund's investments in foreign securities. Foreign securities may also subject the Fund's investments to changes in currency rates. Changes in the value of foreign currencies may make the return on an investment increase or decrease, unrelated to the quality or performance of the investment itself.

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 shares or receive less than the market value when selling 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’s performance.

Emerging Markets Risk: The risks related to investing in foreign securities are generally greater with respect to securities of companies that conduct their business activities in emerging markets or whose securities are traded principally in emerging markets. The risks of investing in emerging markets are elevated under current conditions and include: (i) smaller trading volumes for such securities and limited access to investments in the event of market closures (including due to local holidays), which result in a lack of liquidity and in greater price volatility; (ii) less government regulation, which could lead to market manipulation, and less extensive, transparent and frequent accounting, auditing, recordkeeping, financial reporting and other requirements, which limit the quality and availability of financial information; (iii) the absence of developed legal systems, including structures governing private or foreign investment or allowing for judicial redress (such as limits on rights and remedies available to the Fund) for investment losses and injury to private property; (iv) loss resulting from problems in share registration and custody; (v) sensitivity to adverse political or social events affecting the region where an emerging market is located; (vi) particular sensitivity to economic and political disruptions, including adverse effects stemming from recessions, depressions or other economic crises, or reliance on international or other forms of aid, including trade, taxation and development policies; and (vii) the nationalization of foreign deposits or assets.

Growth Stock Risk: If growth companies do not increase their earnings at a rate expected by investors, the market price of the stock may decline significantly, even if earnings show an absolute increase. Growth company stocks also typically lack the dividend yield that can cushion stock prices in market downturns.

Exchange-Traded Fund Risk: The risks of the Fund owning an ETF generally reflect the risks of owning the securities in which the ETF invests or is designed to track, although lack of liquidity in an ETF could result in it being more volatile than its underlying portfolio securities. Disruptions in the markets for the securities underlying ETFs purchased or sold by the Fund could result in losses on the Fund's investment in ETFs. ETFs also have management fees and transaction costs that may make them more expensive than owning the underlying securities directly.
Risk Lose Money [Text] rr_RiskLoseMoney You can lose money by investing in the Fund.
Risk Not Insured Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution 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 two broad-based securities market indices. The Fund has selected the MSCI ACWI® (All Country World Index) Ex U.S. (Net) as its primary benchmark. The MSCI ACWI® Ex U.S. (Net) is a free float-adjusted market capitalization weighted index that is designed to measure the equity market performance of developed and emerging markets, excluding the U.S. The Fund has selected the MSCI EAFE® Index (Net) as its secondary benchmark. The MSCI EAFE® Index (Net) consists of international stocks representing the developed world outside of North America.

Index returns reflect no deductions for fees, expenses or taxes, except for foreign withholding taxes where applicable.

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 newyorklifeinvestments.com/funds for more recent performance information.

The Fund’s subadvisor changed effective January 1, 2018 due to an organizational restructuring whereby all investment personnel of Cornerstone Capital Management Holdings LLC, the former subadvisor, transitioned to MacKay Shields LLC.

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 Fund has selected the MSCI ACWI® (All Country World Index) Ex U.S. (Net) as its primary benchmark.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress newyorklifeinvestments.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 2012-2021)
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

 

2020, Q2

19.71

%

Worst Quarter

 

2020, Q1

-19.86

%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2021)
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 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 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 Narrative rr_PerformanceTableNarrativeTextBlock 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.
Prospectus Summary | MainStay MacKay International Equity Fund | MSCI ACWI® Ex. U.S. Index  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel MSCI ACWI® Ex. U.S. Index (Net)
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
Since Inception rr_AverageAnnualReturnSinceInception 7.28%
Prospectus Summary | MainStay MacKay International Equity Fund | MSCI EAFE Index®  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel MSCI EAFE Index® (Net)
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
Since Inception rr_AverageAnnualReturnSinceInception 8.03%
Prospectus Summary | MainStay MacKay International Equity Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [1]
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.19%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.33%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 1.18% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock No initial sales charge applies on investments of $1 million or more (and certain other qualified purchases). 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.
1 Year rr_ExpenseExampleYear01 $ 664
3 Years rr_ExpenseExampleYear03 934
5 Years rr_ExpenseExampleYear05 1,225
10 Years rr_ExpenseExampleYear10 $ 2,051
1 Year rr_AverageAnnualReturnYear01 5.70%
5 Years rr_AverageAnnualReturnYear05 13.04%
Since Inception rr_AverageAnnualReturnSinceInception 9.28%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 03, 1995
Prospectus Summary | MainStay MacKay International Equity Fund | INVESTOR CLASS  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 5.00%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [1]
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.57%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.71%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 1.56% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock No initial sales charge applies on investments of $1 million or more (and certain other qualified purchases). 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.
1 Year rr_ExpenseExampleYear01 $ 651
3 Years rr_ExpenseExampleYear03 998
5 Years rr_ExpenseExampleYear05 1,368
10 Years rr_ExpenseExampleYear10 $ 2,407
1 Year rr_AverageAnnualReturnYear01 5.92%
5 Years rr_AverageAnnualReturnYear05 12.64%
Since Inception rr_AverageAnnualReturnSinceInception 8.89%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 28, 2008
Prospectus Summary | MainStay MacKay International Equity Fund | Class B  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [4]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 5.00% [4]
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2],[4]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00% [4]
Other Expenses rr_OtherExpensesOverAssets 0.57% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.46% [4]
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3],[4]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 2.31% [3],[4]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 734
3 Years rr_ExpenseExampleYear03 1,052
5 Years rr_ExpenseExampleYear05 1,497
10 Years rr_ExpenseExampleYear10 2,600
1 Year rr_ExpenseExampleNoRedemptionYear01 234
3 Years rr_ExpenseExampleNoRedemptionYear03 752
5 Years rr_ExpenseExampleNoRedemptionYear05 1,297
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,600
1 Year rr_AverageAnnualReturnYear01 5.94%
5 Years rr_AverageAnnualReturnYear05 12.83%
Since Inception rr_AverageAnnualReturnSinceInception 8.69%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 13, 1994
Prospectus Summary | MainStay MacKay International Equity Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00%
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.57%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.46%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 2.31% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 334
3 Years rr_ExpenseExampleYear03 752
5 Years rr_ExpenseExampleYear05 1,297
10 Years rr_ExpenseExampleYear10 2,600
1 Year rr_ExpenseExampleNoRedemptionYear01 234
3 Years rr_ExpenseExampleNoRedemptionYear03 752
5 Years rr_ExpenseExampleNoRedemptionYear05 1,297
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,600
1 Year rr_AverageAnnualReturnYear01 9.62%
5 Years rr_AverageAnnualReturnYear05 13.06%
Since Inception rr_AverageAnnualReturnSinceInception 8.69%
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 01, 1998
Prospectus Summary | MainStay MacKay International Equity Fund | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.19%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.08%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.23%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 0.85% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 87
3 Years rr_ExpenseExampleYear03 321
5 Years rr_ExpenseExampleYear05 573
10 Years rr_ExpenseExampleYear10 $ 1,296
Annual Return 2012 rr_AnnualReturn2012 19.29%
Annual Return 2013 rr_AnnualReturn2013 15.01%
Annual Return 2014 rr_AnnualReturn2014 (2.96%)
Annual Return 2015 rr_AnnualReturn2015 5.44%
Annual Return 2016 rr_AnnualReturn2016 (5.08%)
Annual Return 2017 rr_AnnualReturn2017 32.34%
Annual Return 2018 rr_AnnualReturn2018 (11.62%)
Annual Return 2019 rr_AnnualReturn2019 24.87%
Annual Return 2020 rr_AnnualReturn2020 20.96%
Annual Return 2021 rr_AnnualReturn2021 12.25%
Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 19.71%
Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (19.86%)
1 Year rr_AverageAnnualReturnYear01 12.25%
5 Years rr_AverageAnnualReturnYear05 14.67%
Since Inception rr_AverageAnnualReturnSinceInception 10.20%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 02, 2004
Prospectus Summary | MainStay MacKay International Equity Fund | Class I | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 8.08%
5 Years rr_AverageAnnualReturnYear05 13.37%
Since Inception rr_AverageAnnualReturnSinceInception 9.57%
Prospectus Summary | MainStay MacKay International Equity Fund | Class I | After Taxes on Distributions and Sales  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 9.05%
5 Years rr_AverageAnnualReturnYear05 11.61%
Since Inception rr_AverageAnnualReturnSinceInception 8.39%
Prospectus Summary | MainStay MacKay International Equity Fund | Class R1  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.29%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.18%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 1.03% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 105
3 Years rr_ExpenseExampleYear03 360
5 Years rr_ExpenseExampleYear05 635
10 Years rr_ExpenseExampleYear10 $ 1,418
1 Year rr_AverageAnnualReturnYear01 12.02%
5 Years rr_AverageAnnualReturnYear05 14.50%
Since Inception rr_AverageAnnualReturnSinceInception 10.06%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 02, 2004
Prospectus Summary | MainStay MacKay International Equity Fund | Class R2  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.29%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.43%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 1.28% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 130
3 Years rr_ExpenseExampleYear03 438
5 Years rr_ExpenseExampleYear05 767
10 Years rr_ExpenseExampleYear10 $ 1,700
1 Year rr_AverageAnnualReturnYear01 11.76%
5 Years rr_AverageAnnualReturnYear05 14.21%
Since Inception rr_AverageAnnualReturnSinceInception 9.79%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 02, 2004
Prospectus Summary | MainStay MacKay International Equity Fund | Class R3  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.29%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.68%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 1.53% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 156
3 Years rr_ExpenseExampleYear03 515
5 Years rr_ExpenseExampleYear05 899
10 Years rr_ExpenseExampleYear10 $ 1,975
1 Year rr_AverageAnnualReturnYear01 11.48%
5 Years rr_AverageAnnualReturnYear05 13.93%
Since Inception rr_AverageAnnualReturnSinceInception 9.52%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 28, 2006
Prospectus Summary | MainStay MacKay International Equity Fund | Class R6  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.09%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.98%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 0.83% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 85
3 Years rr_ExpenseExampleYear03 297
5 Years rr_ExpenseExampleYear05 527
10 Years rr_ExpenseExampleYear10 $ 1,188
1 Year rr_AverageAnnualReturnYear01 12.26%
Since Inception rr_AverageAnnualReturnSinceInception 17.07%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 28, 2019
Prospectus Summary | MainStay MacKay International Equity Fund | SIMPLE CLASS  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.89% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.57%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.96%
Waivers / Reimbursements rr_FeeWaiverOrReimbursementOverAssets (0.15%) [3]
Total Annual Fund Operating Expenses After Waivers / Reimbursements rr_NetExpensesOverAssets 1.81% [3]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2023
1 Year rr_ExpenseExampleYear01 $ 184
3 Years rr_ExpenseExampleYear03 601
5 Years rr_ExpenseExampleYear05 1,043
10 Years rr_ExpenseExampleYear10 $ 2,273
[1] No initial sales charge applies on investments of $1 million or more (and certain other qualified purchases). 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.
[2] The management fee is as follows: 0.89% on assets up to $500 million and 0.85% on assets over $500 million.
[3] 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) for a class do not exceed the following percentage of its average daily net assets: Class I, 0.85% and Class R6, 0.83%. New York Life Investments will apply an equivalent waiver or reimbursement, in an equal number of basis points of the Class R6 shares waiver/reimbursement to the Class A, Investor Class, Class B, Class C, Class R1, Class R2, Class R3 and SIMPLE Class shares. This agreement will remain in effect until February 28, 2023, 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.
[4] Class B shares are closed to all new purchases as well as additional investments by existing Class B shareholders.