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Variable Interest Entities - Investment Products (Details)	3 Months Ended
	Mar. 31, 2013
Variable Interest Entities - Investment Products [Abstract]
Percentage not approached by expected return on any VIE investment	50.00%

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- Definition

Percentage not approached by expected return on any VIE investment

+ References

No definition available.

+ Details

Name:	seic_PercentageNotApproachedByExpectedReturnOnAnyVieInvestment
Namespace Prefix:	seic_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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- Details

Name:	seic_VariableInterestEntitiesInvestmentProductsAbstract
Namespace Prefix:	seic_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration