Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Feb. 28, 2012
MainStay Principal Preservation Fund (Prospectus Summary) | MainStay Principal Preservation Fund
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	MainStay Principal Preservation Fund
Investment Objective, Heading	rr_ObjectiveHeading	Investment Objective
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	The Fund seeks to maximize current income consistent with maintaining liquidity and preserving capital.
Expense, Heading	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense, Narrative	rr_ExpenseNarrativeTextBlock	The table below describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees, Caption	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses, Caption	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Expense Example, Heading	rr_ExpenseExampleHeading	Example
Expense Example, Narrative	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 and then 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.
Expense Example, By Year, Caption	rr_ExpenseExampleByYearCaption	Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Investment Strategy, Heading	rr_StrategyHeading	Principal Investment Strategies
Investment Strategy, Narrative	rr_StrategyNarrativeTextBlock	The Fund invests in short-term, high-quality, U.S. dollar-denominated securities that generally mature in 397 days (13 months) or less. The Fund maintains a dollar-weighted average maturity of 60 days or less and maintains a dollar-weighted average life to maturity of 120 days or less. The Fund seeks to maintain a stable $1.00 net asset value per share. The Fund may invest in obligations issued or guaranteed by the U.S. government or any of its agencies or instrumentalities; U.S. and foreign bank and bank holding company obligations, such as certificates of deposit ("CDs"), bankers' acceptances and Eurodollars; commercial paper; time deposits; repurchase agreements; and corporate debt securities. The Fund may invest in variable rate notes, floaters, and mortgage-related and asset-backed securities. The Fund may also invest in foreign securities that are U.S. dollar-denominated securities of foreign issuers. The Fund will generally invest in obligations that mature in 397 days or less and substantially all of which will be held to maturity. However, the Fund may invest in securities with a face maturity of more than 397 days provided that the security is a variable or floating rate note that meets the applicable guidelines with respect to maturity. Additionally, securities collateralizing repurchase agreements may have maturities in excess of 397 days. Investment Process: New York Life Investments, the Fund's Manager, seeks to achieve the highest yield relative to minimizing risk while also maintaining liquidity and preserving principal. The Manager selects securities based on an analysis of the creditworthiness of the issuer. The Manager works to add value by emphasizing specific securities and sectors of the money market that appear to be attractively priced based upon historical and current yield spread relationships. The Manager may sell a security prior to maturity if it no longer believes that the security will contribute to meeting the investment objective of the Fund.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	rr_RiskNarrativeTextBlock	Stable Net Asset Value Risk: An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund. This could occur because of unusual market conditions or a sudden collapse in the creditworthiness of a company once believed to be an issuer of high-quality, short-term securities. Market Changes Risk: The value of the Fund's investments may change because of broad changes in the markets in which the Fund invests, which could cause the Fund to underperform other funds with similar objectives. From time to time, markets may experience periods of acute stress that may result in increased volatility. Such market conditions tend to add significantly to the risk of short-term volatility in the net asset value of the Fund's shares. Management Risk: The investment strategies, practices and risk analysis used by the Fund's Manager may not produce the desired results. Debt Securities Risk: The risks of investing in debt securities include (without limitation): (i) credit risk, i.e., the issuer may not repay the loan created by the issuance of that debt security; (ii) maturity risk, i.e., a debt security with a longer maturity may fluctuate in value more than one with a shorter maturity; (iii) market risk, i.e., low demand for debt securities may negatively impact their price; (iv) interest rate risk, i.e., when interest rates go up, the value of a debt security goes down, and when interest rates go down, the value of a debt security goes up; (v) selection risk, i.e., the securities selected by the Manager may underperform the market or other securities selected by other funds; and (vi) call risk, i.e., 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. Additional risks associated with an investment in the Fund include the following: (i) not all U.S. government securities are insured or 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; and (ii) the Fund's yield will fluctuate with changes in short-term interest rates. Floaters and Variable Rate Notes Risk: Floaters 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. Such securities also may lose value. Foreign Securities Risk: Investments in foreign securities may be riskier than investments in U.S. securities. Differences between U.S. and foreign regulatory regimes and securities markets, including less stringent investor protections and disclosure standards of some foreign markets, less liquid trading markets, as well as political and economic developments in foreign countries, 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. 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. Mortgage-Backed/Asset-Backed Securities Risk: Prepayment risk is associated with mortgage-backed and asset-backed securities. If interest rates fall, the underlying debt may be repaid ahead of schedule, reducing the value of the Fund's investments. If interest rates rise, there may be fewer prepayments, which would cause the average bond maturity to rise, increasing the potential for the Fund to lose money. 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. The ability of the Fund to successfully utilize these instruments may depend on the ability of the Manager to forecast interest rates and other economic factors correctly. 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. Money Market Fund Regulatory Risk: Money market funds are subject to liquidity, credit quality, and maturity requirements pursuant to Securities and Exchange Commission ("SEC") rules. Because of these requirements, the Fund may achieve a reduced yield relative to the yield achieved prior to the imposition of these requirements. The SEC may adopt additional money market fund regulations in the future, which may impact the operation or performance of the Fund. Yield Risk: There can be no guarantee that the Fund will achieve or maintain any particular level of yield.
Risk, Money Market Fund	rr_RiskMoneyMarketFund	Although the Fund seeks to preserve the value of your investment at $1.00 per share, it is possible to lose money by investing in the Fund.
Risk, Not Insured Depository Institution	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table, Heading	rr_BarChartAndPerformanceTableHeading	Past Performance
Performance, Narrative	rr_PerformanceNarrativeTextBlock	The following bar chart and tables 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 the last ten years. Sales loads 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 for the one-, five- and ten-year periods compare to those of a money market fund average. The Average Lipper Institutional Money Market Fund is an equally weighted performance average adjusted for capital gains distributions and income dividends of all of the institutional money market funds in the Lipper Universe. Lipper Inc., a wholly-owned subsidiary of Reuters Group PLC, is an independent monitor of mutual fund performance. Lipper averages are not class specific. Lipper returns are unaudited. Performance figures for Class I shares reflect the historical performance of the McMorgan Class shares of the McMorgan Principal Preservation Fund for periods prior to November 27, 2007 (a predecessor to the Fund which was subject to a different fee structure, and for which McMorgan & Company LLC served as investment advisor). Past performance is not necessarily an indication of how the Fund will perform in the future. For current yield information, call toll-free: 800-MAINSTAY (624-6782).
Performance, Information Illustrates Variability of Returns	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following bar chart and tables indicate some of the risks of investing in the Fund.
Performance, Availability Phone Number	rr_PerformanceAvailabilityPhone	800-MAINSTAY (624-6782)
Performance, Past Does Not Indicate Future	rr_PerformancePastDoesNotIndicateFuture	Past performance 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 2002-2011)
Bar Chart, Narrative	rr_BarChartNarrativeTextBlock	The bar chart shows you how the Fund's calendar year performance has varied over the last ten years. Sales loads are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart, Does Not Reflect Sales Loads	rr_BarChartDoesNotReflectSalesLoads	Sales loads are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart, Closing	rr_BarChartClosingTextBlock	Best Quarter     3Q/06     1.29 % Worst Quarter    3Q/10     0.00 %
Index No Deduction for Fees, Expenses, Taxes	rr_IndexNoDeductionForFeesExpensesTaxes	reflects no deductions for fees, expenses, or taxes
Average Annual Returns, Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the periods ended December 31, 2011)
MainStay Principal Preservation Fund (Prospectus Summary) | MainStay Principal Preservation Fund | Average Lipper Institutional Money Market Fund
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Average Lipper Institutional Money Market Fund (reflects no deductions for fees, expenses, or taxes)
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	0.04%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	1.57%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	1.88%
MainStay Principal Preservation Fund (Prospectus Summary) | MainStay Principal Preservation Fund | Class I
Risk Return [Abstract]	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_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fees (as an annual percentage of the Fund's average daily net assets)	rr_ManagementFeesOverAssets	0.29%	[1]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.15%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.44%	[2]
Waivers / Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.14%)	[2]
Total Annual Fund Operating Expenses After Waivers / Reimbursements	rr_NetExpensesOverAssets	0.30%	[2]
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-02-28
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	31
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	127
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	232
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	541
Annual Return 2002	rr_AnnualReturn2002	1.58%
Annual Return 2003	rr_AnnualReturn2003	0.97%
Annual Return 2004	rr_AnnualReturn2004	1.13%
Annual Return 2005	rr_AnnualReturn2005	2.98%
Annual Return 2006	rr_AnnualReturn2006	4.87%
Annual Return 2007	rr_AnnualReturn2007	5.07%
Annual Return 2008	rr_AnnualReturn2008	2.52%
Annual Return 2009	rr_AnnualReturn2009	0.62%
Annual Return 2010	rr_AnnualReturn2010	0.01%
Annual Return 2011	rr_AnnualReturn2011	0.01%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2006
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.29%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2010
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Class I
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	0.01%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	1.63%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	1.96%
Money Market, Seven Day Yield, Caption	rr_MoneyMarketSevenDayYieldCaption	7-day current yield
Money Market, Seven Day Yield, Column	rr_MoneyMarketSevenDayYieldColumnName	Class I:
Money Market, Seven Day Yield, Phone Number	rr_MoneyMarketSevenDayYieldPhone	800-MAINSTAY (624-6782)
Money Market, Seven Day Yield	rr_MoneyMarketSevenDayYield	0.01%

[1] The management fee is 0.25%, plus a fee for fund accounting services previously provided for by New York Life Investment Management LLC ("New York Life Investments") under a separate fund counting agreement. This addition to the management fee amounted to 0.04% of the Fund's average daily net assets, but did not result in a net increase in Total Annual Fund Operating Expenses.

[2] 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 Class I shares do not exceed 0.30% of its average daily net assets. This agreement will remain in effect until February 28, 2013, 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.