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Class C Shares Prospectus | SDIT GOVERNMENT II FUND | SDIT GOVERNMENT II FUND - CLASS C
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading SDIT GOVERNMENT II FUND
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] 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 [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)
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 2014-05-31
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:
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
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal market conditions, the Fund invests exclusively in U.S. Treasury obligations and obligations issued or guaranteed as to principal and interest by agencies or instrumentalities of the U.S. Government.


Using a top-down strategy and bottom-up security selection, the sub-adviser (the Sub-Adviser) seeks securities with acceptable maturities (consistent with requirements of the 1940 Act for money market funds) that are marketable and liquid and offer competitive yields. 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 [Text Block] rr_RiskNarrativeTextBlock

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.


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 Money Market Fund [Text] rr_RiskMoneyMarketFund 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 [Text] 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 [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 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 [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 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 [Text] rr_PerformancePastDoesNotIndicateFuture The Fund's past performance is not necessarily an indication of how the Fund will perform in the future.
Annual Return 2003 rr_AnnualReturn2003 0.48%
Annual Return 2004 rr_AnnualReturn2004 0.66%
Annual Return 2005 rr_AnnualReturn2005 2.49%
Annual Return 2006 rr_AnnualReturn2006 4.35%
Annual Return 2007 rr_AnnualReturn2007 4.53%
Annual Return 2008 rr_AnnualReturn2008 1.89%
Annual Return 2009 rr_AnnualReturn2009 0.07%
Annual Return 2010 rr_AnnualReturn2010 0.01%
Annual Return 2011 rr_AnnualReturn2011 0.01%
Annual Return 2012 rr_AnnualReturn2012 0.01%
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Best Quarter: 1.15% (12/31/06)


Worst Quarter: 0.00% (03/31/11)


The Fund's Class C total return from January 1, 2013 to March 31, 2013 was 0.00%.

Year to Date Return, Label rr_YearToDateReturnLabel The Fund's Class C total return from January 1, 2013 to March 31, 2013
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.00%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2006
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.15%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn 0.00%
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

Please call 1-800-DIAL-SEI to obtain the Fund's current 7-day yield.

Caption rr_AverageAnnualReturnCaption Average Annual Total Returns (for the periods ended December 31, 2012)
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.01%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.40%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 1.44%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 2.43%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Nov. 27, 1996
Money Market Seven Day Yield Phone rr_MoneyMarketSevenDayYieldPhone 1-800-DIAL-SEI
[1] Effective May 31, 2013, 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, 2014 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.