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Variable Interest Entities - Investment Products (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 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 | $ 6,525 | $ 6,942 | $ 19,551 | $ 20,620

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