Marketable Securities (Investments Available For Sale) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Available for sale and equity securities, cost	$ 134,561	$ 140,605
Available for sale and equity securities, gross unrealized gains	95	0
Available for sale and equity securities, gross unrealized (losses)	(10,387)	(12,404)
Available for sale and equity securities, fair value	124,269	128,201
Available-for-sale debt securities
Debt Securities, Available-for-sale [Line Items]
Available for sale debt securities, cost	123,288	129,372
Available for sale debt securities, gross unrealized gains	0	0
Available for sale debt securities, gross unrealized (losses)	(10,353)	(12,071)
Available for sale debt securities, fair value	112,935	117,301
SEI-sponsored mutual funds
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, cost	6,216	6,207
Equity securities, FV-NI, gross unrealized gains	89	0
Equity securities, FV-NI, gross unrealized (losses)	(34)	(176)
Equity securities, FV-NI, fair value	6,271	6,031
Equities and other mutual funds
Debt Securities, Available-for-sale [Line Items]
Equity securities, FV-NI, cost	5,057	5,026
Equity securities, FV-NI, gross unrealized gains	6	0
Equity securities, FV-NI, gross unrealized (losses)	0	(157)
Equity securities, FV-NI, fair value	$ 5,063	$ 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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Debt Securities, Available-For-Sale And Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, Before Tax

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Debt Securities, Available-For-Sale And Equity Securities, FV-NI, Cost

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

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Equity Securities, FV-NI, Accumulated Gross Unrealized Loss, 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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Amount, before tax, of unrealized loss 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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Amount 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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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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