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Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Available For Sale and Equity Securities, Cost | $ 140,605 | $ 128,898
Available For Sale and Equity Securities, Gross Unrealized Gains | 0 | 723
Available For Sale and Equity Securities, Gross Unrealized (Losses) | (12,404) | (80)
Available For Sale and Equity Securities, Fair Value | 128,201 | 129,541
Available for sale debt securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Available for sale debt securities, Cost | 129,372 | 117,215
Available for sale debt securities, Gross Unrealized Gains | 0 | 0
Available for sale debt securities, Gross Unrealized (Losses) | (12,071) | (80)
Available for sale debt securities, Fair Value | 117,301 | 117,135
SEI-sponsored mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, Cost | 6,207 | 6,748
Equity securities, FV-NI, Gross Unrealized Gains | 0 | 463
Equity securities, FV-NI, Gross Unrealized (Losses) | (176) | 0
Equity securities, FV-NI, Fair Value | 6,031 | 7,211
Equities and other mutual funds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Equity securities, FV-NI, Cost | 5,026 | 4,935
Equity securities, FV-NI, Gross Unrealized Gains | 0 | 260
Equity securities, FV-NI, Gross Unrealized (Losses) | (157) | 0
Equity securities, FV-NI, Fair Value | $ 4,869 | $ 5,195

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