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Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Available For Sale and Equity Securities, Cost | $ 138,994 | $ 128,898
Available For Sale and Equity Securities, Gross Unrealized Gains | 734 | 723
Available For Sale and Equity Securities, Gross Unrealized (Losses) | (5,011) | (80)
Available For Sale and Equity Securities, Fair Value | 134,717 | 129,541
Available-for-sale debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale debt securities, Cost | 127,804 | 117,215
Available for sale debt securities, Gross Unrealized Gains | 0 | 0
Available for sale debt securities, Gross Unrealized (Losses) | (4,990) | (80)
Available for sale debt securities, Fair Value | 122,814 | 117,135
SEI-sponsored mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, Cost | 6,353 | 6,748
Equity securities, FV-NI, Gross Unrealized Gains | 505 | 463
Equity securities, FV-NI, Gross Unrealized (Losses) | (21) | 0
Equity securities, FV-NI, Fair Value | 6,837 | 7,211
Equities and other mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, Cost | 4,837 | 4,935
Equity securities, FV-NI, Gross Unrealized Gains | 229 | 260
Equity securities, FV-NI, Gross Unrealized (Losses) | 0 | 0
Equity securities, FV-NI, Fair Value | $ 5,066 | $ 5,195

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