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Sale of SEI Asset Korea (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Mar. 28, 2013 | Sep. 30, 2017 | Sep. 30, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |
Gain on sale of subsidiary | $ 0 | $ 0 |  | $ 0 | $ 2,791
SEI Asset Korea Co., Ltd. [Member] |  |  |  |  |
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |
Contingent purchase price from sale of SEI AK |  |  | $ 11,220 |  |
Gain on sale of subsidiary |  |  |  |  | $ 2,791
Gain on sale of subsidiary, diluted earnings per share impact, net |  |  |  |  | $ 0.01

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