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Class Y Prospectus | SIMT TAX-MANAGED LARGE CAP FUND  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading SIMT TAX-MANAGED LARGE CAP FUND
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

High long-term after-tax returns.
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. 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 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

Under normal circumstances, the Tax-Managed Large Cap Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of large companies. For purposes of this Fund, a large company is a company with a market capitalization in the range of companies in the Russell 1000 Index (between $472.7 million and $780.06 billion as of December 31, 2018) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Index are subject to change. The Fund will invest primarily in common stocks, preferred stocks, warrants, American Depositary Receipts (ADRs), real estate investment trusts (REITs) and exchange-traded funds (ETFs). The Fund may also, to a lesser extent, invest in common and preferred stocks of small capitalization companies. The Fund may invest up to 20% of its assets in foreign securities.


The Fund uses a multi-manager approach, relying primarily on a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies and strategies to manage portions of the Fund's portfolio under the general supervision of SEI Investments Management Corporation, the Fund's adviser (SIMC or the Adviser). Assets of the Fund not allocated to Sub-Advisers are managed directly by SIMC. In managing its portion of the Fund's assets, SIMC or each Sub-Adviser may apply a variety of quantitative and/or fundamental investment styles. A quantitative investment style generally involves a systematic or rules-based approach to selecting investments based on specific measurable factors. A fundamental investment style generally involves selecting investments through research and analysis of financial statements, relevant industry and economic data, or other characteristics.


The Fund implements the investment recommendations of SIMC and the Sub-Advisers through the use of an overlay manager appointed by SIMC. Each Sub-Adviser and SIMC provides a model portfolio to the overlay manager on an ongoing basis that represents that Sub-Adviser's or SIMC's recommendation as to the securities to be purchased, sold or retained by the Fund. The overlay manager then constructs a portfolio for the Fund that represents the aggregation of the model portfolios of the Sub-Advisers and SIMC, with the weighting of each Sub-Adviser's model in the total portfolio determined by SIMC.


Pursuant to direction from SIMC, the overlay manager has limited authority to vary from the models, primarily for the purpose of efficient tax management of the Fund's securities transactions. The overlay manager seeks to manage the impact of taxes by, among other things, selling stocks with the highest tax cost first, opportunistically harvesting losses and deferring recognition of taxable gains, where possible. SIMC may also direct the overlay manager to adjust the portfolio to implement SIMC's forward looking views regarding various portfolio characteristics or factors, or for risk management purposes. The overlay manager may also vary the portfolio implementation to seek trading cost efficiencies, portfolio rebalancing or other portfolio construction objectives as directed by SIMC.
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 large capitalization securities may underperform other segments of the equity markets or the equity markets as a whole.


Taxation Risk — The Fund is managed to minimize tax consequences to investors, but will likely earn taxable income and gains from time to time.


Depositary Receipts Risk — Depositary receipts, such as 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.


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 will be subject to the risks associated with the 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. Some REITs may have limited diversification and may be subject to risks inherent in financing a limited number of properties.


Exchange-Traded Funds (ETFs) Risk — The risks of owning shares of an ETF generally reflect the risks of owning the underlying securities the ETF is designed to track, although lack of liquidity in an ETF could result in its value being more volatile than the underlying portfolio securities. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF's expenses.


Warrants Risk — Warrants are instruments that entitle the holder to buy an equity security at a specific price for a specific period of time. Warrants may be more speculative than other types of investments. The price of a warrant may be more volatile than the price of its underlying security, and a warrant may offer greater potential for capital appreciation as well as capital loss. A warrant ceases to have value if it is not exercised prior to its expiration date.


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.


Foreign Investment 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.


Currency Risk — As a result of the Fund's investments in securities or other investments denominated in, and/or receiving revenues in, foreign currencies, the Fund will be subject to currency risk. Currency risk is the risk that foreign currencies will decline in value relative to the U.S. dollar or, in the case of hedging positions, that the U.S. dollar will decline in value relative to the currency hedged. In either event, the dollar value of an investment in the Fund would be adversely affected. 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.


Small Capitalization Risk — Smaller 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 capitalization companies may have limited product lines, markets and financial resources and may depend upon a relatively small management group. Therefore, small capitalization stocks may be more volatile than those of larger companies. Small capitalization stocks may be traded over-the-counter or listed on an exchange.


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 bar chart and the performance table below provide some indication of the risks of investing in the Class Y Shares of the Fund by showing changes in the Fund's performance from year to year for the past ten calendar years and by showing how the Fund's average annual returns for 1, 5 and 10 years, 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 Class Y Shares of the Fund by showing changes in the Fund's performance from year to year for the past ten calendar years and by showing how the Fund's average annual returns for 1, 5 and 10 years, and since the Fund's inception, compare with those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 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: 17.35% (06/30/09)
Worst Quarter: -15.32% (09/30/11)






Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.35%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (15.32%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2018)
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 Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In the event of negative performance, the Fund's returns after taxes on distributions and sale of Fund shares are calculated assuming that an investor has sufficient capital gains of the same character from other investments to offset any capital losses from the sale of Fund shares. As a result, the Fund's returns after taxes on distributions and sale of Fund shares may exceed the Fund's returns before taxes and/or returns after taxes on distributions.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

The Fund's Class Y Shares commenced operations on December 31, 2014. For full calendar years through December 31, 2014, the performance of the Fund's Class F Shares is shown. The Fund's Class F Shares are offered in a separate prospectus. Because Class Y Shares are invested in the same portfolio of securities, returns for Class Y Shares would have been substantially similar to those of Class F Shares, shown here, and would have differed only to the extent that Class Y Shares have lower total annual fund operating expenses than Class F Shares.


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. In the event of negative performance, the Fund's returns after taxes on distributions and sale of Fund shares are calculated assuming that an investor has sufficient capital gains of the same character from other investments to offset any capital losses from the sale of Fund shares. As a result, the Fund's returns after taxes on distributions and sale of Fund shares may exceed the Fund's returns before taxes and/or returns after taxes on distributions.
Class Y Prospectus | SIMT TAX-MANAGED LARGE CAP FUND | Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Label rr_AverageAnnualReturnLabel Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (4.78%) [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 8.21% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 13.28% [1]
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 6.51% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Mar. 05, 1998
Class Y Prospectus | SIMT TAX-MANAGED LARGE CAP FUND | Class Y  
Risk/Return: rr_RiskReturnAbstract  
Management Fees rr_ManagementFeesOverAssets 0.40%
Distribution (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses rr_OtherExpensesOverAssets 0.25%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.65%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 66
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 208
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 362
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 810
Annual Return 2009 rr_AnnualReturn2009 28.92%
Annual Return 2010 rr_AnnualReturn2010 13.70%
Annual Return 2011 rr_AnnualReturn2011 0.43%
Annual Return 2012 rr_AnnualReturn2012 16.35%
Annual Return 2013 rr_AnnualReturn2013 34.73%
Annual Return 2014 rr_AnnualReturn2014 10.99%
Annual Return 2015 rr_AnnualReturn2015 (1.14%)
Annual Return 2016 rr_AnnualReturn2016 8.28%
Annual Return 2017 rr_AnnualReturn2017 21.47%
Annual Return 2018 rr_AnnualReturn2018 (6.02%)
Label rr_AverageAnnualReturnLabel Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (6.02%) [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.29% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 12.09% [1]
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 5.27% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Mar. 05, 1998
Class Y Prospectus | SIMT TAX-MANAGED LARGE CAP 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 (6.38%) [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.88% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 11.67% [1]
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.91% [1]
Class Y Prospectus | SIMT TAX-MANAGED LARGE CAP 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 (3.45%) [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.02% [1]
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 10.24% [1]
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.33% [1]
[1] The Fund's Class Y Shares commenced operations on December 31, 2014. For periods prior to December 31, 2014, the performance of the Fund's Class F Shares has been used. Returns for Class Y Shares would have been substantially similar to those of Class F Shares and would have differed only to the extent that Class Y Shares have lower total annual fund operating expenses than Class F Shares.