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Class F Prospectus | SIMT Large Cap Index Fund  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading SIMT Large Cap Index Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

Seeks to track the performance of a benchmark index that measures the investment return of large-capitalization stocks.

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.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption 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. For the period from January 31, 2018 to September 30, 2018, the Fund's portfolio turnover rate was 6% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 6.00%
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 is managed using a passive investment approach designed to track, before fees and expenses, the performance of the Russell 1000 Index (the Index). Under normal circumstances, the Fund will invest substantially all of its assets (at least 80% of its net assets, plus the amount of any borrowings for investment purposes) in securities (mostly common stocks) of companies that are included in the Index. The Index measures the performance of the large-cap segment of the U.S. equity universe and includes approximately 1000 of the largest securities based on their market capitalization. As of December 31, 2018, the market capitalization of the companies included in the Index ranged from $472.7 million to $780.06 billion. The market capitalization range and the composition of the Index are subject to change.


The Fund's sub-adviser (the Sub-Adviser) selects the Fund's securities under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser). The Sub-Adviser's passive investment strategy seeks to track, before fees and expenses, the return of the index, and therefore differs from an "active" investment strategy where an investment manager buys and sells securities based on its own economic, market or financial analyses. The Sub-Adviser generally will attempt to invest in securities composing the Index in approximately the same proportions as they are represented in the Index (i.e., among other reasons, the Fund could experience high volumes of cash flows or a particular security could be difficult to obtain). In some cases, it may not be possible or practicable to purchase all of the securities composing the Index or to hold them in the same weightings as they are represented in the Index. In those circumstances, the Sub-Adviser may purchase a sampling of stocks in the Index in proportions expected to replicate generally the performance of the Index as a whole and may also use futures contracts to obtain exposure to the equity markets or to a particular security.


The Sub-Adviser may sell securities that are represented in the Index or purchase securities that are not represented in the Index, prior to or after their removal or addition to the Index.


The Fund's investment performance will depend on the Fund's tracking of the Index and the performance of the Index. The Fund's ability to replicate the performance of the Index will depend to some extent on the size and timing of cash flows into and out of the Fund, as well as on the level of the Fund's expenses. Due to these differences, the Fund's performance generally will not be identical to that of the Index.

Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

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


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.


Investment Style Risk — The risk that its investment approach, which attempts to replicate the performance of the Russell 1000 Index, may underperform other segments of the equity markets or the equity markets as a whole. The Fund is also subject to the risk that large capitalization securities may underperform other segments of the equity markets or the equity markets as a whole.


Tracking Error Risk — The risk that the Fund's performance may vary substantially from the performance of the benchmark index it tracks as a result of cash flows, Fund expenses, imperfect correlation between the Fund's investments and the index's components and other factors.


Derivatives Risk — The Fund's use of futures contracts is subject to leverage risk, correlation risk, liquidity risk and market risk. Leverage risk and liquidity risk are described below. 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. Each of these risks could cause the Fund to lose more than the principal amount invested in a derivative instrument. The Fund's use of derivatives may also increase the amount of taxes payable by shareholders. 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.


Liquidity Risk — The risk that certain securities may be difficult or impossible to sell at the time and the price that the Fund would like. The Fund 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.


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.


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 Depository Institution [Text] rr_RiskNotInsuredDepositoryInstitution 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 Fund is new, and therefore does not have a full calendar year of performance. Once the Fund has completed a full calendar year of operations, a bar chart and table will be included that will provide some indication of the risks of investing in the Fund by showing the variability of the Fund's return based on net assets and comparing the Fund's performance to a broad measure of market performance.

Performance One Year or Less [Text] rr_PerformanceOneYearOrLess The Fund is new, and therefore does not have a full calendar year of performance. Once the Fund has completed a full calendar year of operations, a bar chart and table will be included that will provide some indication of the risks of investing in the Fund by showing the variability of the Fund's return based on net assets and comparing the Fund's performance to a broad measure of market performance.
Class F Prospectus | SIMT Large Cap Index Fund | Class F  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.05%
Distribution (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.59%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.64%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 65
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 205
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 357
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 798