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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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