Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	May 31, 2012
SDIT PRIME OBLIGATION FUND (Third Prospectus Summary) | SDIT PRIME OBLIGATION FUND
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	PRIME OBLIGATION FUND
Investment Objective, Heading	rr_ObjectiveHeading	Investment Goal
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	Preserve principal value and maintain a high degree of liquidity while providing current income.
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.
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	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 our 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 Prime Obligation Fund is comprised of short-term U.S. dollar-denominated debt obligations that are rated in one of the two highest rating categories by Nationally Recognized Statistical Rating Organizations or that the Sub-Adviser determines are of comparable quality. Under normal market conditions, the Fund invests in: (i) commercial paper and other short-term corporate obligations of U.S. and foreign issuers (including asset-backed securities) rated in the highest short-term rating category or that the Sub-Adviser determines are of comparable quality; (ii) certificates of deposit, time deposits, bankers' acceptances, bank notes, and other obligations of U.S. savings and loan and thrift institutions, U.S. commercial banks (including foreign branches of such banks) and foreign banks that meet certain asset requirements; (iii) short-term obligations issued by state and local governments; and (iv) U.S. Treasury obligations and obligations issued or guaranteed as to principal and interest by agencies or instrumentalities of the U.S. Government. The Fund may also enter into fully-collateralized repurchase agreements. Using a top-down strategy and bottom-up security selection, the Sub-Adviser seeks securities with acceptable maturities (consistent with requirements of the 1940 Act for money market funds) that are marketable and liquid, offer competitive yields and are issued by issuers that are on a sound financial footing. Currently, the Fund invests only in first-tier securities. The Sub-Adviser also considers factors such as the anticipated level of interest rates and the maturity of individual securities relative to the maturity of the Fund as a whole. The Fund follows the 1940 Act rules about credit quality, maturity and diversification for money market funds. With respect to credit quality and maturity, the Fund's investment guidelines may be more restrictive than the 1940 Act rules applicable to money market funds.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	rr_RiskNarrativeTextBlock	Asset-Backed Securities Risk - Payment of principal and interest on asset-backed securities is dependent largely on the cash flows generated by the assets backing the securities, and asset-backed securities may not have the benefit of any security interest in the related assets. 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. 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. Extension Risk - The risk that rising interest rates may extend the duration of a fixed income security, typically reducing the security's value. 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. In the case of foreign securities, price fluctuations will reflect international economic and political events. Foreign Issuer Risk - The risk that issuers in foreign countries face political and economic events unique to such countries. These events will not necessarily affect the U.S. economy or similar issuers located in the U.S. Interest Rate Risk - The risk that the Fund's yield will decline due to falling interest rates. A rise in interest rates typically causes a fall in the value of fixed income securities in which the Fund invests, while a fall in interest rates typically causes a rise in the value of such securities. During periods when interest rates are low, the Fund's yield will also be low, and the income generated by the Fund may not be sufficient to offset all or a significant portion of the Fund's expenses, which could impair the Fund's ability to provide a positive yield and maintain a stable $1.00 share price. 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, sell other securities instead or forego an investment opportunity, any of which could have a negative effect on Fund management or performance. 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 bond market as a whole. 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. Prepayment Risk - The risk that, with declining interest rates, 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. Redemption Risk - The Fund may experience periods of heavy redemptions that could cause the Fund to liquidate its assets at inopportune times or at a loss or depressed value, particularly during periods of declining or illiquid markets. This could have a significant adverse effect on the Fund's ability to maintain a stable $1.00 share price, and, in extreme circumstances, could cause the Fund to suspend redemptions and liquidate completely. 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. An investment in the Fund is not a bank deposit nor is it insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Although the Fund seeks to maintain a constant price per share of $1.00, you may lose money by investing in the Fund.
Risk, Lose Money	rr_RiskLoseMoney	Although the Fund seeks to maintain a constant price per share of $1.00, you may lose money by investing in the Fund.
Risk, Not Insured Depository Institution	rr_RiskNotInsuredDepositoryInstitution	An investment in the Fund is not a bank deposit nor is it 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	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 the Fund's average annual returns for 1, 5 and 10 years, and since the Fund's inception. The Fund's past performance is not necessarily an indication of how the Fund will perform in the future.
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 the Fund's average annual returns for 1, 5 and 10 years, and since the Fund's inception.
Performance, Past Does Not Indicate Future	rr_PerformancePastDoesNotIndicateFuture	The Fund's past performance is not necessarily an indication of how the Fund will perform in the future.
Bar Chart, Closing	rr_BarChartClosingTextBlock	Best Quarter: 1.20% (09/30/07) Worst Quarter: 0.00% (03/31/11) The Fund's Class C total return from January 1, 2012 to March 31, 2012 was 0.00%.
Performance Table, Closing	rr_PerformanceTableClosingTextBlock	Please call 1-800-DIAL-SEI to obtain the Fund's current 7-day yield.
Average Annual Returns, Caption	rr_AverageAnnualReturnCaption	Average Annual Total Returns (for the periods ended December 31, 2011)
Money Market, Seven Day Yield, Phone Number	rr_MoneyMarketSevenDayYieldPhone	1-800-DIAL-SEI
SDIT PRIME OBLIGATION FUND (Third Prospectus Summary) | SDIT PRIME OBLIGATION FUND | CLASS C
Risk Return [Abstract]	rr_RiskReturnAbstract
Management Fees	rr_ManagementFeesOverAssets	0.07%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.72%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.79%
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.09%)
Total Annual Fund Operating Expenses Less Fee Waivers and Expense Reimbursements	rr_NetExpensesOverAssets	0.70%	[1]
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-05-31
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	72
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	243
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	430
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	970
Annual Return 2002	rr_AnnualReturn2002	1.12%
Annual Return 2003	rr_AnnualReturn2003	0.54%
Annual Return 2004	rr_AnnualReturn2004	0.73%
Annual Return 2005	rr_AnnualReturn2005	2.59%
Annual Return 2006	rr_AnnualReturn2006	4.45%
Annual Return 2007	rr_AnnualReturn2007	4.76%
Annual Return 2008	rr_AnnualReturn2008	2.18%
Annual Return 2009	rr_AnnualReturn2009	0.08%
Annual Return 2010	rr_AnnualReturn2010	0.01%
Annual Return 2011	rr_AnnualReturn2011	0.01%
Year to Date Return, Label	rr_YearToDateReturnLabel	The Fund's Class C total return from January 1, 2012 to March 31, 2012
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	0.00%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2007
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	1.20%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Mar. 31, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	0.00%
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	0.01%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	1.39%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	1.63%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	2.78%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Apr. 30, 1996

[1] Effective May 31, 2012, the Fund's administrator and the Fund's distributor have contractually agreed to waive fees and reimburse expenses for a period of one year in order to keep total annual Fund operating expenses (exclusive of interest from borrowings, brokerage commissions, trustees' fees, taxes and other extraordinary expenses not incurred in the ordinary course of the Fund's business) from exceeding 0.70%. This fee waiver and reimbursement agreement shall remain in effect until May 31, 2013 and, unless earlier terminated, shall be automatically renewed for successive one-year periods thereafter. The agreement may be amended or terminated only with the consent of the Board of Trustees.