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Marketable Securities - Available for Sale and Equity Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale debt securities, cost | $ 142,718 | $ 127,681
Available for sale debt securities, fair value | 135,471 | 118,752
Available for sale and equity securities, cost | 180,339 | 163,409
Available for sale and equity securities, gross unrealized gains | 2,630 | 952
Available for sale and equity securities, gross unrealized (losses) | (7,247) | (8,948)
Available for sale and equity securities, fair value | 175,722 | 155,413
Available-for-sale debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale debt securities, cost | 142,718 | 127,681
Available for sale debt securities, gross unrealized gains | 0 | 0
Available for sale debt securities, gross unrealized (losses) | (7,247) | (8,929)
Available for sale debt securities, fair value | 135,471 | 118,752
SEI-sponsored mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, cost | 32,203 | 30,427
Equity securities, FV-NI, gross unrealized gains | 2,144 | 818
Equity securities, FV-NI, gross unrealized (losses) | 0 | (19)
Equity securities, FV-NI, fair value | 34,347 | 31,226
Equities and other mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, cost | 5,418 | 5,301
Equity securities, FV-NI, gross unrealized gains | 486 | 134
Equity securities, FV-NI, gross unrealized (losses) | 0 | 0
Equity securities, FV-NI, fair value | $ 5,904 | $ 5,435

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