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MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading MainStay Winslow Large Cap Growth 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 tables and examples 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 103 of the Prospectus and Appendix A – Intermediary-Specific Sales Charge Waivers and Discounts, and in the "Alternative Sales Arrangements" section on page 137 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 44% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 44.00%
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

Under normal circumstances, the Fund invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in large capitalization companies, which are companies having a market capitalization in excess of $4 billion at the time of purchase. Typically, Winslow Capital Management, LLC, the Fund's Subadvisor, invests substantially all of the Fund's investable assets in domestic securities. However, the Fund is permitted to invest up to 20% of its net assets in foreign securities. Generally, an issuer of a security 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.

Investment Process: The Fund invests in those companies that the Subadvisor believes will provide an opportunity for achieving superior portfolio returns (i.e., returns in excess of the returns of the average stock mutual fund) over the long term. The Subadvisor seeks to invest in companies that have the potential for above-average future earnings and cash flow growth with management focused on shareholder value.

When purchasing stocks for the Fund, the Subadvisor looks for companies typically having some or all of the following attributes: addressing markets with growth opportunities; leads or gains in market share; identifiable and sustainable competitive advantages; managed by a team that can perpetuate the firm's competitive advantages; high, and preferably rising, returns on invested capital; deploys excess cash flow to enhance shareholder return; and demonstrates sound corporate governance. The Subadvisor may give consideration to certain environmental, social, and governance (“ESG”) criteria when evaluating an investment opportunity.

The Subadvisor takes a "bottom-up" investment approach when selecting investments. This means it bases investment decisions on company specific factors, not general economic conditions.

Under normal market conditions, the Subadvisor employs a sell discipline pursuant to which it may sell some or all of its position in a stock when a stock becomes fully valued, the fundamental business prospects are deteriorating, or the position exceeds limits set by the Subadvisor.
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration Under normal circumstances, the Fund invests at least 80% of its assets (net assets plus any borrowings for investment purposes) in large capitalization companies, which are companies having a market capitalization in excess of $4 billion at the time of purchase. Typically, Winslow Capital Management, LLC, the Fund's Subadvisor, invests substantially all of the Fund's investable assets in domestic securities. However, the Fund is permitted to invest up to 20% of its net assets in foreign securities. Generally, an issuer of a security 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. Investment Process: The Fund invests in those companies that the Subadvisor believes will provide an opportunity for achieving superior portfolio returns (i.e., returns in excess of the returns of the average stock mutual fund) over the long term. The Subadvisor seeks to invest in companies that have the potential for above-average future earnings and cash flow growth with management focused on shareholder value.
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.

Market Capitalization Risk: To the extent the Fund invests in securities issued by small-, mid-, or large-cap companies, the Fund will be subject to the risks associated with securities issued by companies of the applicable market capitalization.  Securities of small-cap and mid-cap companies may be subject to greater price volatility, significantly lower trading volumes, cyclical, static or moderate growth prospects and greater spreads between their bid and ask prices than securities of larger companies. Smaller capitalization companies frequently rely on narrower product lines and niche markets and may be more vulnerable to adverse business or market developments.  Securities issued by larger companies may have less growth potential and may not be able to attain the high growth rates of successful smaller companies, especially during strong economic periods.  In addition, larger companies may be less capable of responding quickly to competitive challenges and industry changes, including those resulting from improvements in technology, and may suffer sharper price declines as a result of earnings disappointments.  There is a risk that the securities issued by companies of a certain market capitalization may underperform the broader market at any given time.

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.

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. These risks may be greater with respect to securities of companies that conduct their business activities in emerging markets or whose securities are traded principally in emerging markets.
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 Russell 1000® Growth Index as its primary benchmark. The Russell 1000® Growth Index measures the performance of the large-cap growth segment of the U.S. equity universe. It includes those Russell 1000® Index companies with higher price-to-book ratios and higher forecasted growth values. The Fund has selected the Standard & Poor’s 500® Index (“S&P 500® Index”) as its secondary benchmark. The S&P 500® Index is widely regarded as the standard index for measuring large-cap U.S. stock market performance.

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.
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 Russell 1000® Growth Index 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 2011-2020)
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

 

Q2/2020

28.27

%

Worst Quarter

 

Q4/2018

-15.98

%
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2020)
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.
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Russell 1000® Growth Index  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deductions for fees, expenses, or taxes
Label rr_AverageAnnualReturnLabel Russell 1000
1 Year rr_AverageAnnualReturnYear01 38.49%
5 Years rr_AverageAnnualReturnYear05 21.00%
Since Inception rr_AverageAnnualReturnSinceInception 17.21%
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | S&P 500® Index  
Risk/Return: rr_RiskReturnAbstract  
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes reflects no deductions for fees, expenses, or taxes
Label rr_AverageAnnualReturnLabel S&P 500
1 Year rr_AverageAnnualReturnYear01 18.40%
5 Years rr_AverageAnnualReturnYear05 15.22%
Since Inception rr_AverageAnnualReturnSinceInception 13.88%
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class A  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLAAX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.10%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.97%
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 $ 644
3 Years rr_ExpenseExampleYear03 842
5 Years rr_ExpenseExampleYear05 1,057
10 Years rr_ExpenseExampleYear10 $ 1,674
1 Year rr_AverageAnnualReturnYear01 29.43%
5 Years rr_AverageAnnualReturnYear05 18.11%
Since Inception rr_AverageAnnualReturnSinceInception 15.21%
Inception Date rr_AverageAnnualReturnInceptionDate Jul. 01, 1995
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | INVESTOR CLASS  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLINX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.23%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.10%
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 $ 607
3 Years rr_ExpenseExampleYear03 832
5 Years rr_ExpenseExampleYear05 1,076
10 Years rr_ExpenseExampleYear10 $ 1,773
1 Year rr_AverageAnnualReturnYear01 29.34%
5 Years rr_AverageAnnualReturnYear05 18.00%
Since Inception rr_AverageAnnualReturnSinceInception 15.13%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 28, 2008
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class B  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLABX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none [3]
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 5.00% [3]
Management Fees (as an annual percentage of the Fund's average daily net assets) rr_ManagementFeesOverAssets 0.62% [2],[3]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00% [3]
Other Expenses rr_OtherExpensesOverAssets 0.23% [3]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.85% [3]
1 Year rr_ExpenseExampleYear01 $ 688
3 Years rr_ExpenseExampleYear03 882
5 Years rr_ExpenseExampleYear05 1,201
10 Years rr_ExpenseExampleYear10 1,973
1 Year rr_ExpenseExampleNoRedemptionYear01 188
3 Years rr_ExpenseExampleNoRedemptionYear03 582
5 Years rr_ExpenseExampleNoRedemptionYear05 1,001
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,973
1 Year rr_AverageAnnualReturnYear01 30.87%
5 Years rr_AverageAnnualReturnYear05 18.25%
Since Inception rr_AverageAnnualReturnSinceInception 14.91%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 01, 2005
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class C  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLACX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses rr_OtherExpensesOverAssets 0.23%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.85%
1 Year rr_ExpenseExampleYear01 $ 288
3 Years rr_ExpenseExampleYear03 582
5 Years rr_ExpenseExampleYear05 1,001
10 Years rr_ExpenseExampleYear10 1,973
1 Year rr_ExpenseExampleNoRedemptionYear01 188
3 Years rr_ExpenseExampleNoRedemptionYear03 582
5 Years rr_ExpenseExampleNoRedemptionYear05 1,001
10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,973
1 Year rr_AverageAnnualReturnYear01 34.97%
5 Years rr_AverageAnnualReturnYear05 18.46%
Since Inception rr_AverageAnnualReturnSinceInception 14.93%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 01, 2005
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class I  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLAIX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.10%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.72%
1 Year rr_ExpenseExampleYear01 $ 74
3 Years rr_ExpenseExampleYear03 230
5 Years rr_ExpenseExampleYear05 401
10 Years rr_ExpenseExampleYear10 $ 894
Annual Return 2011 rr_AnnualReturn2011 (0.19%)
Annual Return 2012 rr_AnnualReturn2012 13.21%
Annual Return 2013 rr_AnnualReturn2013 36.94%
Annual Return 2014 rr_AnnualReturn2014 10.54%
Annual Return 2015 rr_AnnualReturn2015 6.17%
Annual Return 2016 rr_AnnualReturn2016 (2.28%)
Annual Return 2017 rr_AnnualReturn2017 32.39%
Annual Return 2018 rr_AnnualReturn2018 3.74%
Annual Return 2019 rr_AnnualReturn2019 33.67%
Annual Return 2020 rr_AnnualReturn2020 37.38%
Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 28.27%
Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (15.98%)
1 Year rr_AverageAnnualReturnYear01 37.38%
5 Years rr_AverageAnnualReturnYear05 19.77%
Since Inception rr_AverageAnnualReturnSinceInception 16.17%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 01, 2005
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class I | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 35.83%
5 Years rr_AverageAnnualReturnYear05 16.51%
Since Inception rr_AverageAnnualReturnSinceInception 13.83%
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class I | After Taxes on Distributions and Sales  
Risk/Return: rr_RiskReturnAbstract  
1 Year rr_AverageAnnualReturnYear01 23.18%
5 Years rr_AverageAnnualReturnYear05 15.00%
Since Inception rr_AverageAnnualReturnSinceInception 12.81%
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class R1  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLRRX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.20%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.82%
1 Year rr_ExpenseExampleYear01 $ 84
3 Years rr_ExpenseExampleYear03 262
5 Years rr_ExpenseExampleYear05 455
10 Years rr_ExpenseExampleYear10 $ 1,014
1 Year rr_AverageAnnualReturnYear01 37.29%
5 Years rr_AverageAnnualReturnYear05 19.64%
Since Inception rr_AverageAnnualReturnSinceInception 16.04%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 01, 2005
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class R2  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLRTX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.20%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.07%
1 Year rr_ExpenseExampleYear01 $ 109
3 Years rr_ExpenseExampleYear03 340
5 Years rr_ExpenseExampleYear05 590
10 Years rr_ExpenseExampleYear10 $ 1,306
1 Year rr_AverageAnnualReturnYear01 36.92%
5 Years rr_AverageAnnualReturnYear05 19.33%
Since Inception rr_AverageAnnualReturnSinceInception 15.75%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 01, 2005
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class R3  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLGRX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.20%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.32%
1 Year rr_ExpenseExampleYear01 $ 134
3 Years rr_ExpenseExampleYear03 418
5 Years rr_ExpenseExampleYear05 723
10 Years rr_ExpenseExampleYear10 $ 1,590
1 Year rr_AverageAnnualReturnYear01 36.57%
5 Years rr_AverageAnnualReturnYear05 19.04%
Since Inception rr_AverageAnnualReturnSinceInception 15.47%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 28, 2006
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | Class R6  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLRSX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.02%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.64%
1 Year rr_ExpenseExampleYear01 $ 65
3 Years rr_ExpenseExampleYear03 205
5 Years rr_ExpenseExampleYear05 357
10 Years rr_ExpenseExampleYear10 $ 798
1 Year rr_AverageAnnualReturnYear01 37.44%
5 Years rr_AverageAnnualReturnYear05 19.88%
Since Inception rr_AverageAnnualReturnSinceInception 18.20%
Inception Date rr_AverageAnnualReturnInceptionDate Jun. 17, 2013
MainStay Winslow Large Cap Growth Fund (Prospectus Summary) | MainStay Winslow Large Cap Growth Fund | SIMPLE CLASS  
Risk/Return: rr_RiskReturnAbstract  
Trading Symbol dei_TradingSymbol MLRMX
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 0.62% [2]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses rr_OtherExpensesOverAssets 0.23%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.35%
1 Year rr_ExpenseExampleYear01 $ 137
3 Years rr_ExpenseExampleYear03 428
5 Years rr_ExpenseExampleYear05 739
10 Years rr_ExpenseExampleYear10 $ 1,624
[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: 0.75% on assets up to $500 million; 0.725% on assets from $500 million to $750 million; 0.71% on assets from $750 million to $1 billion; 0.70% on assets from $1 billion to $2 billion; 0.66% on assets from $2 billion to $3 billion; 0.61% on assets from $3 billion to $7 billion; 0.585% on assets from $7 billion to $9 billion; and 0.575% on assets over $9 billion.
[3] Class B shares are closed to all new purchases as well as additional investments by existing Class B shareholders.