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Variable Interest Entities - Investment Products (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
SEI Sponsored Open Ended Money Market Mutual Funds [Member] |  |  |
Financial Support for Nonconsolidated Legal Entity [Line Items] |  |  |
Fees waived according to expense limitation agreements | $ 27,434 | $ 41,227 | $ 55,713

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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://www.xbrl.org/2003/role/presentationRef -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 + Details
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