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Sale of SEI Asset Korea (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 28, 2013 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Gain on sale of subsidiary |  | $ 0 | $ 2,791 | $ 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 | $ 2,791
Gain on sale of subsidiary, diluted earnings per share impact, net |  |  | $ 0.01 | $ 0.01

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