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Class Y Prospectus | SIMT Dynamic Asset Allocation Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading SIMT Dynamic Asset Allocation Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Long-term total return.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold Fund shares.
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 5% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 5.00%
Expense Example [Heading] rr_ExpenseExampleHeading EXAMPLE
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This 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 [Text] rr_ExpenseExampleByYearCaption 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 employs a dynamic investment strategy seeking to achieve, over time, a total return in excess of the broad U.S. equity market by selecting investments from among a broad range of asset classes or market exposures based upon SEI Investments Management Corporation's (SIMC or the Adviser) expectations of risk and return. Asset classes or market exposures in which the Fund may invest include U.S. and foreign equities and bonds, currencies, and investment exposures to various market characteristics such as interest rates or volatility. The Fund's sub-adviser (the Sub-Adviser) selects the Fund's securities under the general supervision of SIMC. Assets of the Fund not allocated to the Sub-Adviser are managed directly by SIMC.


The asset classes and market exposures used, and the Fund's allocations among them, are determined based on SIMC's views of fundamental, technical or valuation measures and may be dynamically adjusted (i.e. actively adjusted over long or short periods of time). The Fund may at any particular point in time be diversified across many exposures or concentrated in a limited number of exposures, including, possibly, a single asset class or market exposure.


Although the Fund will seek to achieve excess total return through its dynamic investment selection, it will also normally maintain, as a primary component of its strategy, passive exposure to the large capitalization U.S. equity market. To the extent that the Fund is not dynamically invested in other asset classes or market exposures, the Fund's assets will generally be passively invested in a portfolio of securities designed to track, before fees and expenses, the performance of the large capitalization U.S. equity market.


The Fund may obtain asset class or market exposures by investing directly (e.g., in equity and fixed income securities and other instruments) or indirectly (e.g., through the use of other pooled investment vehicles, a wholly-owned subsidiary or derivative instruments, principally futures contracts, forward contracts, options and swaps). The particular types of securities and other instruments in which the Fund may invest are further described below.


Equity Securities. The Fund may invest in equity securities, including common stocks, preferred stocks, convertible securities, warrants (including equity-linked warrants) and depositary receipts of U.S. and non-U.S. issuers (including emerging markets) of various market capitalizations and industries.


Fixed Income Securities. The Fund may invest in fixed income securities that are investment or non-investment grade (also known as "junk bonds"), U.S.- or foreign-issued (including emerging markets), and corporate- or government-issued. The Fund's fixed income investments may include corporate bonds and debentures, commercial paper, exchange traded notes (ETNs), money market instruments, repurchase and reverse repurchase agreements, zero coupon bonds, structured notes, obligations of foreign governments, and obligations of either supranational entities issued or guaranteed by certain banks and entities organized to restructure the outstanding debt of such issuers.


The Fund's fixed income investments may also include U.S. Treasury obligations, obligations issued by agencies or instrumentalities of the U.S. Government and Treasury Inflation Protected Securities (TIPS) and other inflation-linked debt securities of both U.S. and non-U.S. governments and corporations.


The Fund may invest in fixed, variable and floating rate fixed income instruments. The Fund's portfolio and the Fund's investments in particular fixed income securities are not subject to any maturity or duration restrictions.


Other Instruments. The Fund may also invest in real estate investment trusts (REITs) and securities issued by U.S. and non-U.S. real estate companies.


Pooled Investment Vehicles. In addition to direct investment in securities and other instruments, the Fund may invest in affiliated and unaffiliated funds, including open-end funds, money market funds, closed-end funds and exchange-traded funds (ETFs), to obtain the Fund's desired exposure to a particular asset class.


Derivative and Commodity Instruments. The Fund may also purchase or sell futures contracts, forward contracts, options and swaps (including swaptions, caps, floors or collars) for return enhancement or hedging purposes or to obtain the Fund's desired exposure to a particular asset class or market exposure. Futures contracts, forward contracts and swaps may be used to synthetically obtain exposure to securities or baskets of securities and to manage the Fund's interest rate duration and yield curve exposure. These derivatives may also be used to mitigate the Fund's overall level of risk and/or the Fund's exposure to the risk of particular types of securities or market segments. The Fund may purchase or sell futures contracts (and options on futures contracts) on U.S. Government securities for return enhancement and hedging purposes. The Fund may purchase and sell forward contracts on currencies or securities for return enhancement and hedging purposes. Interest rate swaps are further used to manage the Fund's yield spread sensitivity.


Swaps may be used for return enhancement or hedging purposes. Securities index and single security swaps may be used to manage the inflation-adjusted return of the Fund or to more efficiently gain exposure to a particular security or basket of securities. The Fund may buy credit default swaps in an attempt to manage credit risk where the Fund has credit exposure to an issuer, and the Fund may sell credit default swaps to more efficiently gain credit exposure to a security or basket of securities. The Fund may also, to a lesser extent, purchase or sell put or call options on securities, indexes or currencies for return enhancement or hedging purposes or to obtain the Fund's desired exposure to a particular asset class or market exposure.


The Fund may seek to gain exposure to the commodity markets, in whole or in part, through investments in a wholly owned subsidiary of the Fund organized under the laws of the Cayman Islands (Subsidiary). The Subsidiary, unlike the Fund, may invest to a significant extent in commodities, commodity contracts, commodity investments and commodity-linked derivative instruments. The Subsidiary may also invest in other instruments in which the Fund is permitted to invest, either as investments or to serve as margin or collateral for its derivative positions. The Fund may invest up to 25% of its total assets in the Subsidiary. The Subsidiary is advised by SIMC.


Currency Exposure. The Fund may invest in U.S. dollar and non-U.S. dollar denominated securities. SIMC or the Sub-Adviser may also seek to enhance the Fund's return by actively managing the Fund's foreign currency exposure. In managing the Fund's currency exposure, SIMC or the Sub-Adviser may buy and sell currencies (i.e., take long or short positions) using futures, options and foreign currency forward contracts. The Fund may take long and short positions in foreign currencies in excess of the value of the Fund's assets denominated in a particular currency or when the Fund does not own assets denominated in that currency. The Fund may also engage in currency transactions in an attempt to take advantage of certain inefficiencies in the currency exchange market, to increase its exposure to a foreign currency or to shift exposure to foreign currency fluctuations from one currency to another. In managing the Fund's currency exposure from foreign securities, SIMC or the Sub-Adviser may buy and sell currencies for hedging or for speculative purposes.


Short Sales. The Sub-Adviser may engage in short sales in an attempt to capitalize on equity securities that it or SIMC believes will underperform the market or their peers. When the Sub-Adviser sells securities short, it may invest the proceeds from the short sales in an attempt to enhance returns. This strategy may effectively result in the Fund having a leveraged investment portfolio, which results in greater potential for loss.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Equity Market Risk — The risk that the market value of a security may move up and down, sometimes rapidly and unpredictably. Equity market risk may affect a single issuer, an industry, a sector or the equity or bond market as a whole.


Fixed Income Market Risk — The prices of the Fund's fixed income securities respond to economic developments, particularly interest rate changes, as well as to perceptions about the creditworthiness of individual issuers, including governments and their agencies. Generally, the Fund's fixed income securities will decrease in value if interest rates rise and vice versa. In a low interest rate environment, risks associated with rising rates are heightened. Declines in dealer market-making capacity as a result of structural or regulatory changes could decrease liquidity and/or increase volatility in the fixed income markets. In the case of foreign securities, price fluctuations will reflect international economic and political events, as well as changes in currency valuations relative to the U.S. dollar. In response to these events, the Fund's value may fluctuate and/or the Fund may experience increased redemptions from shareholders, which may impact the Fund's liquidity or force the Fund to sell securities into a declining or illiquid market.


Duration Risk — The longer-term securities in which the Fund may invest tend to be more volatile than shorter-term securities. A portfolio with a longer average portfolio duration is more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration.


Leverage Risk — The Fund's use of derivatives may result in the Fund's total investment exposure substantially exceeding the value of its portfolio securities and the Fund's investment returns depending substantially on the performance of securities that the Fund may not directly own. The use of leverage can amplify the effects of market volatility on the Fund's share price and may also cause the Fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations. The Fund's use of leverage may result in a heightened risk of investment loss.


Interest Rate Risk — The risk that a rise in interest rates will cause a fall in the value of fixed income securities, including U.S. Government securities, in which the Fund invests. A low interest rate environment may present greater interest rate risk because there may be a greater likelihood of rates increasing and rates may increase more rapidly.


Derivatives Risk — The Fund's use of futures contracts, options, forward contracts and swaps is subject to market risk, leverage risk, correlation risk and liquidity risk. Leverage risk is described above and liquidity risk is described below. Many over-the-counter (OTC) derivative instruments will not have liquidity beyond the counterparty to the instrument. Market risk is the risk that the market value of an investment may move up and down, sometimes rapidly and unpredictably. Correlation risk is the risk that changes in the value of the derivative may not correlate perfectly with the underlying asset, rate or index. The Fund's use of forward contracts and swap agreements is also subject to credit risk and valuation risk. Credit risk is described below. Valuation risk is the risk that the derivative may be difficult to value and/or valued incorrectly. Each of these risks could cause the Fund to lose more than the principal amount invested in a derivative instrument. Some derivatives have the potential for unlimited loss, regardless of the size of the Fund's initial investment. The other parties to certain derivative contracts present the same types of credit risk as issuers of fixed income securities. The Fund's use of derivatives may also increase the amount of taxes payable by shareholders. Both U.S. and non-U.S. regulators are in the process of adopting and implementing regulations governing derivatives markets, the ultimate impact of which remains unclear.


Credit Risk — The risk that the issuer of a security or the counterparty to a contract will default or otherwise become unable to honor a financial obligation.


Currency Risk — Due to the Fund's active positions in currencies, it will be subject to the risk that currency exchange rates may fluctuate in response to, among other things, changes in interest rates, intervention (or failure to intervene) by U.S. or foreign governments, central banks or supranational entities, or by the imposition of currency controls or other political developments in the United States or abroad.


Inflation Protected Securities Risk — The value of inflation protected securities, including TIPS, generally will fluctuate in response to changes in "real" interest rates, generally decreasing when real interest rates rise and increasing when real interest rates fall. Real interest rates represent nominal (or stated) interest rates reduced by the expected impact of inflation. In addition, interest payments on inflation-indexed securities will generally vary up or down along with the rate of inflation.


Commodity-Linked Securities Risk — Investments in commodity-linked securities may be more volatile and less liquid than direct investments in the underlying commodities themselves. Commodity-related equity returns can also be affected by the issuer's financial structure or the performance of unrelated businesses.


U.S. Government Securities Risk — Although U.S. Government securities are considered to be among the safest investments, they are not guaranteed against price movements due to changing interest rates. Obligations issued by some U.S. Government agencies are backed by the U.S. Treasury, while others are backed solely by the ability of the agency to borrow from the U.S. Treasury or by the agency's own resources.


Corporate Fixed Income Securities Risk — Corporate fixed income securities respond to economic developments, especially changes in interest rates, as well as perceptions of the creditworthiness and business prospects of individual issuers.


Below Investment Grade Securities Risk (Junk Bonds) — Fixed income securities rated below investment grade (junk bonds) involve greater risks of default or downgrade and are generally more volatile than investment grade securities because the prospect for repayment of principal and interest of many of these securities is speculative. These risks may be increased in foreign and emerging markets.


Commercial Paper Risk — Commercial paper is a short-term obligation with a maturity generally ranging from one to 270 days and is issued by U.S. or foreign companies or other entities in order to finance their current operations. Such investments are unsecured and usually discounted from their value at maturity. The value of commercial paper may be affected by changes in the credit rating or financial condition of the issuing entities and will tend to fall when interest rates rise and rise when interest rates fall. Asset-backed commercial paper may be issued by structured investment vehicles or other conduits that are organized to issue the commercial paper and to purchase trade receivables or other financial assets. The repayment of asset-backed commercial paper depends primarily on the cash collections received from such issuer's underlying asset portfolio and the issuer's ability to issue new asset-backed commercial paper.


Foreign Investment/Emerging Markets Risk — The risk that non-U.S. securities may be subject to additional risks due to, among other things, political, social and economic developments abroad, currency movements, and different legal, regulatory and tax environments. These additional risks may be heightened with respect to emerging market countries because political turmoil and rapid changes in economic conditions are more likely to occur in these countries.


Foreign Sovereign Debt Securities Risk — The risks that: (i) the governmental entity that controls the repayment of sovereign debt may not be willing or able to repay the principal and/or interest when it becomes due because of factors such as debt service burden, political constraints, cash flow problems and other national economic factors; (ii) governments may default on their debt securities, which may require holders of such securities to participate in debt rescheduling or additional lending to defaulting governments; and (iii) there is no bankruptcy proceeding by which defaulted sovereign debt may be collected in whole or in part.


Repurchase Agreement Risk — Although repurchase agreement transactions must be fully collateralized at all times, they generally create leverage and involve some counterparty risk to the Fund whereby a defaulting counterparty could delay or prevent the Fund's recovery of collateral.


Liquidity Risk — The risk that certain securities may be difficult or impossible to sell at the time and the price that the seller would like. The seller may have to lower the price of the security, sell other securities instead or forego an investment opportunity, any of which could have a negative effect on Fund management or performance


Extension Risk — The risk that rising interest rates may extend the duration of a fixed income security, typically reducing the security's value.


Prepayment Risk — The risk that, in a declining interest rate environment, fixed income securities with stated interest rates may have the principal paid earlier than expected, requiring the Fund to invest the proceeds at generally lower interest rates.


Opportunity Risk — The risk of missing out on an investment opportunity because the assets necessary to take advantage of it are tied up in other investments.


Short Sales Risk — A short sale involves the sale of a security that the Fund does not own in the expectation of purchasing the same security (or a security exchangeable therefore) at a later date at a lower price. Short sales expose the Fund to the risk that it will be required to buy the security sold short (also known as "covering" the short position) at a time when the security has appreciated in value, thus resulting in a loss to the Fund. Investment in short sales may also cause the Fund to incur expenses related to borrowing securities. Reinvesting proceeds received from short selling may create leverage, which can amplify the effects of market volatility on the Fund's share price. In addition, shorting a future contract may require posting only a margin that may amount to less than the notional exposure of the contract. Such a practice may exacerbate the loss in a case of adverse price action.


Real Estate Industry Risk — Securities of companies principally engaged in the real estate industry may be subject to the risks associated with direct ownership of real estate. Risks commonly associated with the direct ownership of real estate include fluctuations in the value of underlying properties, defaults by borrowers or tenants, changes in interest rates and risks related to general or local economic conditions.


Real Estate Investment Trusts (REITs) Risk — REITs are trusts that invest primarily in commercial real estate or real estate-related loans. The Fund's investments in REITs are subject to the risks associated with the direct ownership of real estate, which are discussed above. Some REITs may have limited diversification and may be subject to risks inherent in financing a limited number of properties.


Exchange-Traded Notes (ETNs) Risk — The value of an ETN is subject to the credit risk of the issuer. There may not be an active trading market available for some ETNs. Additionally, trading of ETNs may be halted or the ETN may be delisted by the listing exchange.


Small and Medium Capitalization Risk — The risk that small and medium capitalization companies in which the Fund may invest may be more vulnerable to adverse business or economic events than larger, more established companies. In particular, small and medium capitalization companies may have limited product lines, markets and financial resources and may depend upon a relatively small management group. Therefore, small capitalization and medium capitalization stocks may be more volatile than those of larger companies. Small capitalization and medium capitalization stocks may be traded over-the-counter. OTC stocks may trade less frequently and in smaller volume than exchange-listed stocks and may have more price volatility than that of exchange-listed stocks.


Large Capitalization Risk — The risk that larger, more established companies may be unable to respond quickly to new competitive challenges such as changes in technology and consumer tastes. Larger companies also may not be able to attain the high growth rates of successful smaller companies.


Depositary Receipts Risk — Depositary receipts, such as American Depositary Receipts (ADRs), are certificates evidencing ownership of shares of a foreign issuer that are issued by depositary banks and generally trade on an established market. Depositary receipts are subject to many of the risks associated with investing directly in foreign securities, including, among other things, political, social and economic developments abroad, currency movements and different legal, regulatory and tax environments.


Tax Risk — To the extent the Fund invests in commodities and certain commodity-linked derivative instruments directly, it will seek to restrict its income from such investments that do not generate qualifying income, to a maximum of 10% of its gross income to permit the Fund to qualify as a regulated investment company (RIC) under Subchapter M of the Internal Revenue Code of 1986, as amended (the Code). Failure to comply with the qualifying income test would have significant negative tax consequences to Fund shareholders.


The Fund will gain most of its exposure to the commodities markets through its investment in a Subsidiary, which invests in commodity investments and derivative instruments. The Fund's investment in the Subsidiary is expected to provide the Fund with exposure to the commodities markets within the limitations of the federal tax requirements of Subchapter M of the Code for qualification as a RIC. The Fund expects its income attributable to its investment in the Subsidiary to be treated as "qualifying income" for tax purposes. The Adviser will ensure that no more than 25% of the Fund's assets are invested in the Subsidiary.


Investment Company and Exchange-Traded Funds (ETFs) Risk — When the Fund invests in an investment company, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the investment company's expenses. In addition, while the risks of owning shares of an investment company generally reflect the risks of owning the underlying investments of the investment company, the Fund may be subject to additional or different risks than if the Fund had invested directly in the underlying investments. For example, the lack of liquidity in an ETF could result in its value being more volatile than the underlying portfolio securities. Closed-end investment companies issue a fixed number of shares that trade on a stock exchange or over-the-counter at a premium or a discount to their net asset value. As a result, a closed-end fund's share price fluctuates based on what another investor is willing to pay rather than on the market value of the securities in the fund.


Investment in the Subsidiary Risk — A Subsidiary is not registered under the Investment Company Act of 1940 (the 1940 Act) and, unless otherwise noted in this prospectus, is not subject to all of the investor protections of the 1940 Act. Thus, the Fund, as an investor in a Subsidiary, will not have all of the protections offered to investors in registered investment companies. In addition, changes in the laws of the United States and/or the Cayman Islands, under which the Fund and a Subsidiary, respectively, are organized, could result in the inability of the Fund and/or a Subsidiary to operate as intended and could negatively affect the Fund and its shareholders.


Convertible and Preferred Securities Risk — Convertible and preferred securities have many of the same characteristics as stocks, including many of the same risks. In addition, convertible securities may be more sensitive to changes in interest rates than stocks. Convertible securities may also have credit ratings below investment grade, meaning that they carry a higher risk of failure by the issuer to pay principal and/or interest when due.


LIBOR Replacement Risk — The elimination of the London Inter-Bank Offered Rate (LIBOR) may adversely affect the interest rates on, and value of, certain Fund investments for which the value is tied to LIBOR. It remains unclear if LIBOR will continue to exist in its current form or will be modified after 2021, or whether the market will adopt one or more alternative rates. It will be difficult to predict the full impact of the transition away from LIBOR on the Fund until new reference rates and market practices have been commercially accepted.


Investing in the Fund involves risk, and there is no guarantee that the Fund will achieve its investment goal. You could lose money on your investment in the Fund, just as you could with other investments. An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Lose Money [Text] rr_RiskLoseMoney You could lose money on your investment in the Fund, just as you could with other investments.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The bar chart and the performance table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year for the past four calendar years and by showing how the Fund's average annual returns for 1 year and since the Fund's inception, compare with those of a broad measure of market performance. The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. For current performance information, please call 1-800-DIAL-SEI.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and the performance table below provide some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year for the past four calendar years and by showing how the Fund's average annual returns for 1 year and since the Fund's inception, compare with those of a broad measure of market performance.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress 1-800-DIAL-SEI
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter: 12.80% (03/31/19)

Worst Quarter: -13.10% (12/31/18)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 12.80%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (13.10%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2019)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Your actual after-tax returns will depend on your tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Class Y Prospectus | SIMT Dynamic Asset Allocation Fund | Standard & Poor's 500 Composite Stock Price Index Return (reflects no deduction for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Standard & Poor's 500 Composite Stock Price Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 31.49%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 12.42%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jul. 30, 2015
Class Y Prospectus | SIMT Dynamic Asset Allocation Fund | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Distribution (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Total Other Expenses rr_OtherExpensesOverAssets 0.33%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.93%
Total Management Fees rr_NetExpensesOverAssets 0.60%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 95
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 296
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 515
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,143
Annual Return 2016 rr_AnnualReturn2016 11.68%
Annual Return 2017 rr_AnnualReturn2017 19.29%
Annual Return 2018 rr_AnnualReturn2018 (8.10%)
Annual Return 2019 rr_AnnualReturn2019 27.13%
Label rr_AverageAnnualReturnLabel Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 27.13%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 9.82%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jul. 30, 2015
Management of the Fund ck0000804239_Component1ManagementFeesOverAssets 0.60%
Management of the Subsidiary ck0000804239_Component2ManagementFeesOverAssets none
Other Expenses of the Fund ck0000804239_Component4OtherExpensesOverAssets 0.33%
Other Expenses of the Subsidiary ck0000804239_Component5OtherExpensesOverAssets none
Class Y Prospectus | SIMT Dynamic Asset Allocation Fund | Class Y | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 26.58%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 9.28%
Class Y Prospectus | SIMT Dynamic Asset Allocation Fund | Class Y | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 16.46%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 7.59%