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Investments and Other Marketable Securities - Available-for-Sale and Equity Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale debt securities, Cost Amount | $ 172,986 | $ 154,211
Available for sale debt securities, Fair Value | 167,821 | 143,126
Available for sale and equity securities, Cost Amount | 223,327 | 192,794
Available for sale and equity securities, Gross Unrealized Gains | 3,153 | 1,947
Available for sale and equity securities, Gross Unrealized (Losses) | (5,165) | (11,085)
Available for sale and equity securities, Fair Value | 221,315 | 183,656
Available-for-sale debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available-for-sale debt securities, Cost Amount | 172,986 | 154,211
Available-for-sale debt securities, Gross Unrealized Gains | 0 | 0
Available-for-sale debt securities, Gross Unrealized (Losses) | (5,165) | (11,085)
Available for sale debt securities, Fair Value | 167,821 | 143,126
SEI-sponsored investment products |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, Cost Amount | 44,348 | 33,029
Equity securities, FV-NI, Gross Unrealized Gains | 2,470 | 1,615
Equity securities, FV-NI, Gross Unrealized (Losses) | 0 | 0
Equity securities, FV-NI, Fair Value | 46,818 | 34,644
Equities and other investment products |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, Cost Amount | 5,993 | 5,554
Equity securities, FV-NI, Gross Unrealized Gains | 683 | 332
Equity securities, FV-NI, Gross Unrealized (Losses) | 0 | 0
Equity securities, FV-NI, Fair Value | $ 6,676 | $ 5,886

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