Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Jan. 31, 2012
SIMT TAX-MANAGED SMALL/MID CAP FUND (First Prospectus Summary) | SIMT TAX-MANAGED SMALL/MID CAP FUND
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	TAX-MANAGED SMALL/MID CAP FUND
Investment Objective, Heading	rr_ObjectiveHeading	Investment Goal
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	High long-term after-tax returns.
Expense, Heading	rr_ExpenseHeading	Fees and Expenses
Expense, Narrative	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Fund shares.
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)
Portfolio Turnover, Heading	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover	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 105% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	105.00%
Expense Example, Heading	rr_ExpenseExampleHeading	EXAMPLE
Expense Example, Narrative	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	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	Under normal circumstances, the Tax-Managed Small/Mid Cap Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of small and medium capitalization companies, including ETFs. The Fund will invest primarily in common stocks of U.S. companies with market capitalizations in the range of companies in the Russell 2500 Index (between approximately $16 million and $9.69 billion as of December 31, 2011) at the time of purchase. The market capitalization range and the composition of the Russell 2500 Index are subject to change. The Fund's investments in equity securities may include common and preferred stocks and, to a lesser extent, REITs and securities of large capitalization companies. The Fund uses a multi-manager approach, relying upon a number of Sub-Advisers to manage portions of the Fund's portfolio under the general supervision of SIMC. In managing its portion of the Fund's assets, each Sub-Adviser generally applies either a growth-oriented, a value-oriented or a blended approach to selecting investments. Growth-oriented managers generally select stocks they believe have attractive growth and appreciation potential in light of such characteristics as revenue and earnings growth, expectations from sell-side analysts and relative valuation, while value-oriented managers generally select stocks they believe are attractively valued in light of fundamental characteristics such as earnings, capital structure and/or return on invested capital. Generally, the Sub-Advisers will look to manage the impact of taxes by controlling portfolio turnover levels, selling stocks with the highest tax cost first and opportunistically harvesting losses to offset gains where possible.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	rr_RiskNarrativeTextBlock	Equity Market Risk - The risk that stock prices will fall over short or extended periods of time. 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. Investment Style Risk - The risk that small or medium capitalization securities may underperform other segments of the equity markets or the equity markets as a whole. 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, sell other securities instead or forego an investment opportunity, any of which could have a negative effect on Fund management or performance. 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. Small and Medium Capitalization Companies Risk - The smaller and medium capitalization companies in which the Fund invests 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 and medium capitalization stocks may be more volatile than those of larger companies. Small and medium capitalization stocks may be traded over-the-counter or listed on an exchange. Taxation Risk - The Fund is managed to minimize tax consequences to investors, but will likely earn taxable income and gains from time to time. Loss of money is a risk of investing in the Fund.
Risk, Lose Money	rr_RiskLoseMoney	Loss of money is a risk of investing in the Fund.
Bar Chart and Performance Table, Heading	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance, Narrative	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 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, compared 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	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 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, compared with those of a broad measure of market performance.
Performance, Availability Phone Number	rr_PerformanceAvailabilityPhone	1-800-DIAL-SEI
Performance, Past Does Not Indicate Future	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	rr_BarChartClosingTextBlock	Best Quarter: 22.54% (06/30/03) Worst Quarter: -27.26% (12/31/08)
Performance Table, Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for the periods ended December 31, 2011)
Index No Deduction for Fees, Expenses, Taxes	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.
SIMT TAX-MANAGED SMALL/MID CAP FUND (First Prospectus Summary) | SIMT TAX-MANAGED SMALL/MID CAP FUND | Russell 2500 Index Return
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Russell 2500 Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	(2.51%)
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	1.24%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	6.57%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	5.89%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 31, 2000	[1]
SIMT TAX-MANAGED SMALL/MID CAP FUND (First Prospectus Summary) | SIMT TAX-MANAGED SMALL/MID CAP FUND | Class A
Risk Return [Abstract]	rr_RiskReturnAbstract
Redemption Fee (applies to a redemption, or series of redemptions, from a single identifiable source that, in the aggregate, exceeds $25 million within any thirty (30) day period)	rr_RedemptionFeeOverRedemption	(1.00%)
Management Fees	rr_ManagementFeesOverAssets	0.65%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.64%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.29%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	131
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	409
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	708
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	1,556
Annual Return 2002	rr_AnnualReturn2002	(19.12%)
Annual Return 2003	rr_AnnualReturn2003	48.70%
Annual Return 2004	rr_AnnualReturn2004	16.62%
Annual Return 2005	rr_AnnualReturn2005	6.84%
Annual Return 2006	rr_AnnualReturn2006	12.34%
Annual Return 2007	rr_AnnualReturn2007	1.65%
Annual Return 2008	rr_AnnualReturn2008	(41.16%)
Annual Return 2009	rr_AnnualReturn2009	35.78%
Annual Return 2010	rr_AnnualReturn2010	24.07%
Annual Return 2011	rr_AnnualReturn2011	(4.41%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2003
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	22.54%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(27.26%)
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Class A Return Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	(4.41%)
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	(0.75%)
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	4.95%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	3.97%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 31, 2000
SIMT TAX-MANAGED SMALL/MID CAP FUND (First Prospectus Summary) | SIMT TAX-MANAGED SMALL/MID CAP FUND | Class A | After Taxes on Distributions
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Class A Return After Taxes on Distributions
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	(4.45%)
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	(1.00%)
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	4.48%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	3.55%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 31, 2000
SIMT TAX-MANAGED SMALL/MID CAP FUND (First Prospectus Summary) | SIMT TAX-MANAGED SMALL/MID CAP FUND | Class A | After Taxes on Distributions and Sales
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Class A Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	(2.81%)
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	(0.65%)
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	4.27%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	3.41%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Oct. 31, 2000

[1] Index returns are shown from October 31, 2000.