Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Available for sale and equity securities, cost	$ 128,086	$ 140,605
Available for sale and equity securities, gross unrealized gains	496	0
Available for sale and equity securities, gross unrealized (losses)	(11,791)	(12,404)
Available for sale and equity securities, fair value	116,791	128,201
Available-for-sale debt securities
Debt Securities, Available-for-sale [Line Items]
Available for sale debt securities, cost	117,727	129,372
Available for sale debt securities, gross unrealized gains	0	0
Available for sale debt securities, gross unrealized (losses)	(11,762)	(12,071)
Available for sale debt securities, fair value	105,965	117,301
SEI-sponsored mutual funds
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, cost	5,315	6,207
Equity securities, FV-NI, gross unrealized gains	206	0
Equity securities, FV-NI, gross unrealized (losses)	(29)	(176)
Equity securities, FV-NI, fair value	5,492	6,031
Equities and other mutual funds
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, cost	5,044	5,026
Equity securities, FV-NI, gross unrealized gains	290	0
Equity securities, FV-NI, gross unrealized (losses)	0	(157)
Equity securities, FV-NI, fair value	$ 5,334	$ 4,869

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Debt Securities, Available-For-Sale And Equity Securities, FV-NI, Accumulated Gross Unrealized Gain, Before Tax

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Equity Securities, FV-NI, Accumulated Gross Unrealized Gain, Before Tax

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

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