v3.26.3
Label Element Value
SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk/Return [Heading] oef_RiskReturnHeading ULTRA SHORT DURATION BOND FUND
Objective [Heading] oef_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] oef_ObjectivePrimaryTextBlock

Provide higher current income than that typically offered by a money market fund while maintaining a high degree of liquidity and a correspondingly higher risk of principal volatility.

Expense Heading [Optional Text] oef_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] oef_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy, hold, and sell Fund shares. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in this table and examples below.

Operating Expenses Caption [Optional Text] oef_OperatingExpensesCaption ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Expense Example [Heading] oef_ExpenseExampleHeading EXAMPLE
Expense Example Narrative [Text Block] oef_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 or hold 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] oef_ExpenseExampleByYearCaption Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Portfolio Turnover [Heading] oef_PortfolioTurnoverHeading PORTFOLIO TURNOVER
Portfolio Turnover [Text Block] oef_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 73% of the average value of its portfolio.

Portfolio Turnover, Rate oef_PortfolioTurnoverRate 73.00%
Strategy [Heading] oef_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] oef_StrategyNarrativeTextBlock

Under normal circumstances, the Ultra Short Duration Bond Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in investment grade U.S. dollar-denominated debt instruments, including: (i) commercial paper and other corporate obligations; (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) U.S. Treasury obligations and obligations issued or guaranteed as to principal and interest by agencies or instrumentalities of the U.S. Government; (iv) mortgage-backed securities; (v) asset-backed securities; (vi) collateralized debt obligations and collateralized loan obligations; (vii) fully-collateralized repurchase agreements involving any of the foregoing obligations; and (viii) U.S. dollar-denominated instruments of foreign issuers. In addition, the Fund may invest in futures contracts, options, swaps and other similar instruments. The primary derivatives used by the Fund are futures contracts, options, interest rate swaps and credit default swaps. The Fund will primarily use futures contracts for hedging purposes to manage the Fund’s exposure to interest rate risk. There will be times when the Fund utilizes futures contracts to take an active position to either add or reduce the interest rate sensitivity of the Fund. The Fund will primarily use options and swaps to either mitigate the Fund’s overall level of risk or to gain exposure to a particular fixed income security or segment of the fixed income market.

Using a top-down strategy and bottom-up security selection, one or more sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) seeks attractively-valued securities that offer competitive yields and that are issued by issuers that are on a sound financial footing. The Sub-Adviser also considers factors such as the anticipated level of interest rates, relative valuations and yield spreads among various sectors and the duration of the Fund’s entire portfolio. Duration measures the price sensitivity of a fixed income security to changes in interest rates. For example, a five-year duration means that the fixed income security will decrease in value by 5% if interest rates rise 1% and increase in value by 5% if interest rates fall 1%. While the Fund may invest in securities with any maturity or duration, the Fund will maintain a portfolio duration of 18 months or less under normal market conditions.

To achieve its investment goal, the Fund may invest in one or more SEI-sponsored funds to pursue its investment strategies in an efficient manner. The Fund may invest in a SEI-sponsored fund only if the SEI-sponsored fund invests in securities and pursues investment strategies that are consistent with the Fund’s investment goal and strategy.

The Fund uses a multi-manager approach under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser), the Fund’s adviser, allocating its assets among Sub-Advisers using different investment strategies designed to provide current income consistent with the preservation of capital.

Summary of Definition of Rule 35d-1 Term in Fund Name [Text Block] fnd_NmRule35d1TermDfnSmryTextBlock Using a top-down strategy and bottom-up security selection, one or more sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) seeks attractively-valued securities that offer competitive yields and that are issued by issuers that are on a sound financial footing. The Sub-Adviser also considers factors such as the anticipated level of interest rates, relative valuations and yield spreads among various sectors and the duration of the Fund’s entire portfolio. Duration measures the price sensitivity of a fixed income security to changes in interest rates. For example, a five-year duration means that the fixed income security will decrease in value by 5% if interest rates rise 1% and increase in value by 5% if interest rates fall 1%. While the Fund may invest in securities with any maturity or duration, the Fund will maintain a portfolio duration of 18 months or less under normal market conditions.
Summary of Selection Criteria for Rule 35d-1 Term in Fund Name [Text Block] fnd_NmRule35d1TermSlctnCritSmryTextBlock The Fund uses a multi-manager approach under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser), the Fund’s adviser, allocating its assets among Sub-Advisers using different investment strategies designed to provide current income consistent with the preservation of capital.
Rule 35d-1 Eighty Percent Investment Policy [Text Block] fnd_NmRule35d1EightyPctInvstmntPlcyTextBlock

Under normal circumstances, the Ultra Short Duration Bond Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in investment grade U.S. dollar-denominated debt instruments, including: (i) commercial paper and other corporate obligations; (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) U.S. Treasury obligations and obligations issued or guaranteed as to principal and interest by agencies or instrumentalities of the U.S. Government; (iv) mortgage-backed securities; (v) asset-backed securities; (vi) collateralized debt obligations and collateralized loan obligations; (vii) fully-collateralized repurchase agreements involving any of the foregoing obligations; and (viii) U.S. dollar-denominated instruments of foreign issuers.
Bar Chart and Performance Table [Heading] oef_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] oef_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, compare

with those of a broad measure of market performance. The performance information shown is based on full calendar years. 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] oef_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, compare with those of a broad measure of market performance.
Performance Additional Market Index [Text] oef_PerformanceAdditionalMarketIndex This table compares the Fund’s average annual total returns to those of a broad-based securities market index and an additional index with characteristics relevant to the Fund’s investment strategy.
Performance Availability Phone [Text] oef_PerformanceAvailabilityPhone 1‑800-DIAL-SEI
Performance Past Does Not Indicate Future [Text] oef_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] oef_BarChartClosingTextBlock
Best Quarter: 2.63% (6/30/20)
Worst Quarter: -1.30% (3/31/20)
The Fund's total return from January 1, 2026 to June 30, 2026 was 1.60%.
Year to Date Return, Label [Optional Text] oef_YearToDateReturnLabel total return
Bar Chart, Year to Date Return, Date oef_BarChartYearToDateReturnDate Jun. 30, 2026
Bar Chart, Year to Date Return oef_BarChartYearToDateReturn 1.60%
Highest Quarterly Return, Label [Optional Text] oef_HighestQuarterlyReturnLabel Best Quarter:
Highest Quarterly Return, Date oef_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return oef_BarChartHighestQuarterlyReturn 2.63%
Lowest Quarterly Return, Label [Optional Text] oef_LowestQuarterlyReturnLabel Worst Quarter:
Lowest Quarterly Return, Date oef_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return oef_BarChartLowestQuarterlyReturn (1.30%)
Performance Table Heading oef_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2025)
Index No Deduction for Fees, Expenses, or Taxes [Text] oef_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate oef_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 oef_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 oef_PerformanceTableNarrativeTextBlock

This table compares the Fund’s average annual total returns to those of a broad-based securities market index and an additional index with characteristics relevant to the Fund’s investment strategy.

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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Risk Lose Money [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock You could lose money on your investment in the Fund, just as you could with other investments.
SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Risk Not Insured [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock 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.
SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Market Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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. Generally, the Fund’s fixed income securities will decrease in value if interest rates rise and vice versa. In a low interest rate environment, risks associated with rising rates are heightened. Declines in dealer market-making capacity as a result of structural or regulatory changes could decrease liquidity and/or increase volatility in the fixed income markets. Markets for fixed income securities may decline significantly in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value, public perceptions concerning these developments, and adverse investor sentiment or publicity. Similarly, environmental and public health risks, such as natural disasters, epidemics, pandemics or widespread fear that such events may occur, may impact markets adversely and cause market volatility in both the short- and long-term. In response to these events, the Fund’s value may fluctuate and/or the Fund may experience increased redemptions from shareholders, which may impact the Fund’s liquidity or force the Fund to sell securities into a declining or illiquid market.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Duration Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Duration Risk — The longer-term securities in which the Fund may invest tend to be more volatile than shorter-term securities. A portfolio with a longer average portfolio duration is more sensitive to changes in interest rates than a portfolio with a shorter average portfolio duration.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Investment Style Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Investment Style Risk — The risk that short-duration fixed income securities may underperform other segments of the fixed income markets or the fixed income markets as a whole.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Interest Rate Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Interest Rate Risk — The risk that a change in interest rates will cause a fall in the value of fixed income securities, including U.S. Government securities, in which a Fund invests. Generally, the value of the Fund’s fixed income securities will vary inversely with the direction of prevailing interest rates. Changing interest rates may have unpredictable effects on the markets and may affect the value and liquidity of instruments held by the Fund. 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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Corporate Fixed Income Securities Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Commercial Paper Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Commercial Paper Risk — Commercial paper is a short-term obligation with a maturity generally ranging from one to 270 days and is issued by U.S. or foreign companies or other entities in order to finance their current operations. Such investments are unsecured and usually discounted from their value at maturity. The value of commercial paper may be affected by changes in the credit rating or financial condition of the issuing entities and will tend to fall when interest rates rise and rise when interest rates fall. Asset-backed commercial paper may be issued by structured investment vehicles or other conduits that are organized to issue the commercial paper and to purchase trade receivables or other financial assets. The repayment of asset-backed commercial paper depends primarily on the cash collections received from such an issuer’s underlying asset portfolio and the issuer’s ability to issue new asset-backed commercial paper.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Foreign Investment Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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, tax, accounting and audit environments.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | U.S. Government Securities Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

U.S. Government Securities Risk — Although U.S. Government securities are considered to be among the safest investments, they are still subject to the credit risk of the U.S. Government and 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. No assurance can be given that the U.S. Government will provide financial support to its agencies and instrumentalities if it is not obligated by law to do so.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Asset-Backed Securities Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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. Securitization trusts generally do not have any assets or sources of funds other than receivables and related property they own, and asset-backed securities are generally not insured or guaranteed by the related sponsor or any other entity. Asset-backed securities may be more illiquid than more conventional types of fixed income securities that the Fund may acquire.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Mortgage-Backed Securities Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Mortgage-Backed Securities Risk — Mortgage-backed securities are affected significantly by the rate of prepayments and modifications of the mortgage loans backing those securities, as well as by other factors such as borrower defaults, delinquencies, realized or liquidation losses and other shortfalls. Mortgage-backed securities are particularly sensitive to prepayment risk, which is described below, given that the term to

maturity for mortgage loans is generally substantially longer than the expected lives of those securities; however, the timing and amount of prepayments cannot be accurately predicted. The timing of changes in the rate of prepayments of the mortgage loans may significantly affect the Fund’s actual yield to maturity on any mortgage-backed securities, even if the average rate of principal payments is consistent with the Fund’s expectation. Along with prepayment risk, mortgage-backed securities are significantly affected by interest rate risk, which is described above. In a low interest rate environment, mortgage loan prepayments would generally be expected to increase due to factors such as refinancings and loan modifications at lower interest rates. In contrast, if prevailing interest rates rise, prepayments of mortgage loans would generally be expected to decline and therefore extend the weighted average lives of mortgage-backed securities held or acquired by the Fund.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Repurchase Agreements and Reverse Repurchase Agreements Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Repurchase Agreements and Reverse Repurchase Agreements Risk — In the event of the insolvency of the counterparty to a repurchase agreement or reverse repurchase agreement, recovery of the repurchase price owed to the Fund or, in the case of a reverse repurchase agreement, the securities sold by the Fund, may be delayed. Because reverse repurchase agreements may be considered to be the practical equivalent of borrowing funds, they constitute a form of leverage. If the Fund reinvests the proceeds of a reverse repurchase agreement at a rate lower than the cost of the agreement, entering into the agreement will lower the Fund’s yield.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Derivatives Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Derivatives Risk — The Fund’s use of futures contracts, options, interest rate swaps and credit default swaps is subject to market risk, leverage risk, correlation risk and liquidity risk. Leverage risk and liquidity risk are described below and market risk is described above. Many over-the-counter (OTC) derivative instruments will not have liquidity beyond the counterparty to the instrument. Correlation risk is the risk that changes in the value of the derivative may not correlate perfectly with the underlying asset, rate or index. The Fund’s use of forward contracts, credit-linked notes and swaps is also subject to credit risk and valuation risk. Credit risk is described below. Valuation risk is the risk that the derivative may be difficult to value and/or valued incorrectly. Each of these risks could cause the Fund to lose more than the principal amount invested in a derivative instrument. Some derivatives have the potential for unlimited loss, regardless of the size of the Fund’s initial investment. The other parties to certain derivative contracts present the same types of credit risk as issuers of fixed income securities. The Fund’s use of derivatives may also increase the amount of taxes payable by shareholders. Both U.S. and non-U.S. regulators have adopted and implemented regulations governing derivatives markets, the ultimate impact of which remains unclear.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Investment Company Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Investment Company Risk — When the Fund invests in an investment company, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the investment company’s expenses. In addition, while the risks of owning shares of an investment company generally reflect the risks of owning the underlying investments of the investment company, the Fund may be subject to additional or different risks than if the Fund had invested directly in the underlying investments. For example, the lack of liquidity in an exchange-traded fund could result in its value being more volatile than the underlying portfolio securities.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Investing in Limited Recourse Obligations Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Investing in Limited Recourse Obligations Risk — Collateralized debt obligation (CDO) and collateralized loan obligation (CLO) securities are non-recourse obligations of their issuer payable solely from the related underlying collateral or its proceeds. Therefore, as a holder of CDOs and CLOs, the Fund must rely only on distributions on the underlying collateral or related proceeds for payment. If distributions on the underlying collateral are insufficient to make payments on the CDO or CLO securities, no other assets will be available

for payment of the deficiency. As a result, the amount and timing of interest and principal payments in respect of CDO and CLO securities will depend on the performance and characteristics of the related underlying collateral.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Currency Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Currency Risk — As a result of the Fund’s investments in securities 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. Due to the Fund’s investments in securities denominated in foreign currencies, it will be subject to the risk that 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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Liquidity Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Opportunity Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Credit Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Extension Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Extension Risk — The risk that rising interest rates may extend the duration of a fixed income security, typically reducing the security’s value.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Prepayment Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Prepayment Risk — The risk that, in a declining interest rate environment, 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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | Leverage Risk [Member]  
Prospectus [Line Items] oef_ProspectusLineItems  
Risk [Text Block] oef_RiskTextBlock

Leverage Risk — The Fund’s use of derivatives and repurchase agreements (which effectively constitute a form of borrowing) 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.

SIIT Ultra Short Duration Bond Fund | ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A  
Prospectus [Line Items] oef_ProspectusLineItems  
Management Fees (as a percentage of Assets) oef_ManagementFeesOverAssets 0.15%
Distribution and Service (12b-1) Fees oef_DistributionAndService12b1FeesOverAssets 0.00%
Other Expenses (as a percentage of Assets): oef_OtherExpensesOverAssets 0.09%
Expenses (as a percentage of Assets) oef_ExpensesOverAssets 0.24%
Expense Example, with Redemption, 1 Year oef_ExpenseExampleYear01 $ 25
Expense Example, with Redemption, 3 Years oef_ExpenseExampleYear03 77
Expense Example, with Redemption, 5 Years oef_ExpenseExampleYear05 135
Expense Example, with Redemption, 10 Years oef_ExpenseExampleYear10 $ 306
ULTRA SHORT DURATION BOND FUND | Bloomberg Short U.S. Treasury 9‑12 Month Index Return (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Bloomberg Short U.S. Treasury 9‑12 Month Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Return, Percent oef_AvgAnnlRtrPct 4.40%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.78%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.18%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.55%
ULTRA SHORT DURATION BOND FUND | Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Bloomberg U.S. Aggregate Bond Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Return, Percent oef_AvgAnnlRtrPct 7.30%
Average Annual Return, Percent oef_AvgAnnlRtrPct (0.36%)
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.01%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.42%
ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A  
Prospectus [Line Items] oef_ProspectusLineItems  
Annual Return [Percent] oef_AnnlRtrPct 1.85%
Annual Return [Percent] oef_AnnlRtrPct 1.77%
Annual Return [Percent] oef_AnnlRtrPct 1.87%
Annual Return [Percent] oef_AnnlRtrPct 3.56%
Annual Return [Percent] oef_AnnlRtrPct 2.04%
Annual Return [Percent] oef_AnnlRtrPct 0.25%
Annual Return [Percent] oef_AnnlRtrPct (0.92%)
Annual Return [Percent] oef_AnnlRtrPct 6.23%
Annual Return [Percent] oef_AnnlRtrPct 5.72%
Annual Return [Percent] oef_AnnlRtrPct 5.07%
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Return Before Taxes
Average Annual Return, Percent oef_AvgAnnlRtrPct 5.07%
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.23%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.72%
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.19%
Performance Inception Date oef_PerfInceptionDate Feb. 28, 2011
ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Return After Taxes on Distributions
Average Annual Return, Percent oef_AvgAnnlRtrPct 3.14%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.87%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.61%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.29%
ULTRA SHORT DURATION BOND FUND | SIIT Ultra Short Duration Bond Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] oef_ProspectusLineItems  
Average Annual Return, Label [Optional Text] oef_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Return, Percent oef_AvgAnnlRtrPct 2.98%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.88%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.60%
Average Annual Return, Percent oef_AvgAnnlRtrPct 1.29%