Label	Element	Value
Class F Prospectus \| SIMT Conservative Income Fund
Risk/Return:	rr_RiskReturnAbstract
Supplement to Prospectus [Text Block]	rr_SupplementToProspectusTextBlock	SEI INSTITUTIONAL MANAGED TRUST Conservative Income Fund (the "Fund") Supplement Dated July 10, 2019 to the Class F Prospectus, dated January 31, 2019, as amended on April 1, 2019, April 4, 2019, June 27, 2019 and July 1, 2019 (the "Prospectus") This Supplement provides new and additional information beyond that contained in the Prospectus and should be read in conjunction with such Prospectus.
Risk/Return [Heading]	rr_RiskReturnHeading	SIMT Conservative Income Fund
Bar Chart Narrative [Text Block]	rr_BarChartNarrativeTextBlock	In the Fund Summary for the Fund, under the heading titled "Performance Information," the bar chart showing changes in the Fund's performance from year to year for the past two calendar years is hereby deleted and replaced with the following:
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	There are no other changes to the Prospectus. PLEASE RETAIN THIS SUPPLEMENT FOR FUTURE REFERENCE
Class F Prospectus \| SIMT Conservative Income Fund \| Class F
Risk/Return:	rr_RiskReturnAbstract
Annual Return 2017	rr_AnnualReturn2017	0.99%
Annual Return 2018	rr_AnnualReturn2018	1.86%

If the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 4
-Subsection b
-Paragraph 2
-Subparagraph ii

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 4
-Subsection b
-Paragraph 2
-Subparagraph ii

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 4
-Subsection b
-Paragraph 2
-Subparagraph ii

+ Details

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- Definition

Provide a brief explanation of how the information illustrates the variability of the Fund's returns (e.g., by stating that the information provides some indication of the risks of investing in the Fund by showing changes in the Fund's performance from year to year and by showing how the Fund's average annual returns for 1, 5, and 10 years compare with those of a broad measure of market performance). Provide a statement to the effect that the Fund's past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 4
-Subsection b
-Paragraph 2
-Subparagraph i

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Risk/Return Summary Investment Objectives/Goals Include the following information, in plain English under rule 421(d) under the Securities Act, in the order and subject matter indicated

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A
-Chapter A
-Section 2

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- Definition

This element contains the text of a prospectus supplement (submission type 497) not already contained in an element containing amended text or other data from a previous submission.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Form
-Number N-1A

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