Variable Interest Entities - Investment Products (Details)	12 Months Ended
Dec. 31, 2012
Variable Interest Entities - Investment Products [Abstract]
Percentage not approached by expected return on any VIE investment	50.00%

Percentage not approached by expected return on any VIE investment

No definition available.

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