Variable Interest Entities - Investment Products (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
SEI-Sponsored Open-Ended Money Market Mutual Funds
Financial Support for Nonconsolidated Legal Entity [Line Items]
Fees waived according to expense limitation agreements	$ 6,372	$ 6,606	$ 13,026	$ 13,678

Amount of financial support provided to a nonconsolidated legal entity that is required to comply with or operate in accordance with requirements that are similar to those included in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 20
-Section 50
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66023616&loc=SL35737432-115832

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 15
-Paragraph 12
-Subparagraph (f)(2)
-URI http://asc.fasb.org/extlink&oid=66022390&loc=d3e923-111674

Name:	us-gaap_NonconsolidatedLegalEntityFinancialSupportAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration