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Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale and equity securities, cost | $ 134,561 | $ 140,605
Available for sale and equity securities, gross unrealized gains | 95 | 0
Available for sale and equity securities, gross unrealized (losses) | (10,387) | (12,404)
Available for sale and equity securities, fair value | 124,269 | 128,201
Available-for-sale debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale debt securities, cost | 123,288 | 129,372
Available for sale debt securities, gross unrealized gains | 0 | 0
Available for sale debt securities, gross unrealized (losses) | (10,353) | (12,071)
Available for sale debt securities, fair value | 112,935 | 117,301
SEI-sponsored mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, cost | 6,216 | 6,207
Equity securities, FV-NI, gross unrealized gains | 89 | 0
Equity securities, FV-NI, gross unrealized (losses) | (34) | (176)
Equity securities, FV-NI, fair value | 6,271 | 6,031
Equities and other mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, cost | 5,057 | 5,026
Equity securities, FV-NI, gross unrealized gains | 6 | 0
Equity securities, FV-NI, gross unrealized (losses) | 0 | (157)
Equity securities, FV-NI, fair value | $ 5,063 | $ 4,869

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