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Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Available for sale debt securities, Cost	$ 127,681	$ 129,372
Available for sale debt securities, Fair Value	118,752	117,301
Available For Sale and Equity Securities, Cost	163,409	140,605
Available For Sale and Equity Securities, Gross Unrealized Gains	952	0
Available For Sale and Equity Securities, Gross Unrealized (Losses)	(8,948)	(12,404)
Available For Sale and Equity Securities, Fair Value	155,413	128,201
Available for sale debt securities
Debt Securities, Available-for-sale [Line Items]
Available for sale debt securities, Cost	127,681	129,372
Available for sale debt securities, Gross Unrealized Gains	0	0
Available for sale debt securities, Gross Unrealized (Losses)	(8,929)	(12,071)
Available for sale debt securities, Fair Value	118,752	117,301
SEI-sponsored mutual funds
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, Cost	30,427	6,207
Equity securities, FV-NI, Gross Unrealized Gains	818	0
Equity securities, FV-NI, Gross Unrealized (Losses)	(19)	(176)
Equity securities, FV-NI, Fair Value	31,226	6,031
Equities and other mutual funds
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, Cost	5,301	5,026
Equity securities, FV-NI, Gross Unrealized Gains	134	0
Equity securities, FV-NI, Gross Unrealized (Losses)	0	(157)
Equity securities, FV-NI, Fair Value	$ 5,435	$ 4,869

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