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Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2025 | Mar. 31, 2024 | Dec. 31, 2024
Summary of Significant Accounting Policies [Line Items] |  |  |
Cash and cash equivalents invested in SEI-sponsored money market funds | $ 710,685 |  | $ 839,891
Restricted cash | 302 |  | 302
Capitalized software development costs | 7,362 | $ 6,277 |
Net book value of capitalized software | $ 235,696 |  | 236,023
Anti-dilutive employee stock options (in shares) | 5,834 | 10,912 |
Anti-dilutive employee stock options (in USD per share) | $ 65.95 | $ 61.05 |
Investment Managers |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Capitalized software development costs | $ 2,987 | $ 2,482 |
Capitalized software in progress | 33,800 |  |
SEI Wealth Platform |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Capitalized software development costs | 4,375 | 3,795 |
Net book value of capitalized software | 201,896 |  |
Capitalized software in progress | 4,375 |  |
Amortization expense related to the SEI Wealth Platform | $ 7,099 | 6,757 |
SEI Wealth Platform | Weighted Average |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Estimated useful life of the SEI Wealth Platform | 8 years |  |
SEI-Sponsored Open-Ended Money Market Mutual Funds |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Cash and cash equivalents invested in SEI-sponsored money market funds | $ 261,392 |  | 341,311
SEI Investments (Europe) Limited |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Restricted cash | 250 |  | 250
SEI Investments Distribution Co. (SIDCO) |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Restricted cash | 52 |  | $ 52
SEI-Sponsored Open-Ended Money Market Mutual Funds |  |  |
Summary of Significant Accounting Policies [Line Items] |  |  |
Fees waived | $ 4,133 | $ 4,299 |

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 260 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482662/260-10-50-1 + Details
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