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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016 | Dec. 31, 2015
Cash and cash equivalents invested in SEI-sponsored money market funds | $ 660,362 | $ 594,767 | $ 660,362 | $ 594,767 | $ 695,701 | $ 679,661
Restricted cash | 3,502 |  | 3,502 |  | 3,500 |
Capitalized software development costs |  |  | 33,292 | $ 19,597 |  |
Net book value of capitalized software | $ 304,673 |  | $ 304,673 |  | 295,867 |
Anti-dilutive employee stock options | 11,255 | 10,388 | 11,267 | 10,447 |  |
Anti-dilutive employee stock options, per share | $ 37.68 | $ 34.06 | $ 37.69 | $ 34.05 |  |
SEI Wealth Platform [Member] |  |  |  |  |  |
Capitalized software development costs |  |  | $ 27,994 | $ 16,120 |  |
Net book value of capitalized software | $ 283,867 |  | 283,867 |  |  |
Estimated useful life of the SEI Wealth Platform | 15 years |  |  |  |  |
Amortization expense related to the SEI Wealth Platform |  |  | 24,486 | 22,049 |  |
SEI Wealth Platform [Member] | Weighted Average [Member] |  |  |  |  |  |
Estimated useful life of the SEI Wealth Platform | 5 years |  |  |  |  |
Application for Investment Managers segment [Member] |  |  |  |  |  |
Capitalized software development costs |  |  | 5,298 | $ 3,477 |  |
Net book value of capitalized software | $ 20,806 |  | 20,806 |  |  |
SEI Investments (Europe) Limited [Member] |  |  |  |  |  |
Restricted cash | 3,000 |  | 3,000 |  | 3,000 |
SEI Investments Distribution Co. (SIDCO) [Member] |  |  |  |  |  |
Restricted cash | 502 |  | 502 |  | 500 |
SEI-Sponsored Open-Ended Money Market Mutual Funds [Member] |  |  |  |  |  |
Cash and cash equivalents invested in SEI-sponsored money market funds | $ 230,721 |  | $ 230,721 |  | $ 374,760 |

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic net Income or Loss per outstanding limited partnership unit in the future and that were not included in the computation of diluted net income per limited partnership unit, because to do so would increase net income per unit amounts or decrease loss per unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1533-109256 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=96947427&loc=d3e1536-109256 + Details
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- Definition Additions made to capitalized computer software costs during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16265-109275 + Details
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