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Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands | Jun. 30, 2022 | Dec. 31, 2021
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale and equity securities, cost | $ 130,843 | $ 128,898
Available for sale and equity securities, gross unrealized gains | 0 | 723
Available for sale and equity securities, gross unrealized (losses) | (9,161) | (80)
Available for sale and equity securities, fair value | 121,682 | 129,541
Available-for-sale debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale debt securities, cost | 119,702 | 117,215
Available for sale debt securities, gross unrealized gains | 0 | 0
Available for sale debt securities, gross unrealized (losses) | (8,832) | (80)
Available for sale debt securities, fair value | 110,870 | 117,135
SEI-sponsored mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, cost | 6,271 | 6,748
Equity securities, FV-NI, gross unrealized gains | 0 | 463
Equity securities, FV-NI, gross unrealized (losses) | (249) | 0
Equity securities, FV-NI, fair value | 6,022 | 7,211
Equities and other mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, cost | 4,870 | 4,935
Equity securities, FV-NI, gross unrealized gains | 0 | 260
Equity securities, FV-NI, gross unrealized (losses) | (80) | 0
Equity securities, FV-NI, fair value | $ 4,790 | $ 5,195

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