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Marketable Securities (Narrative) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Schedule of Investments [Line Items]
Cash equivalents at fair value	$ 458,521,000		$ 458,521,000		$ 422,838,000
Net unrealized gains (loss)	(6,801,000)		(6,801,000)		(62,000)
Net unrealized gains (losses) income tax expense (benefit)	(2,031,000)		(2,031,000)		(18,000)
Available-for-sale securities, gross realized gains			0	$ 0
Mutual funds and equities, gross realized gains			7,000	613,000
Mutual funds and equities, gross realized loss			658,000	59,000
Other long-term investments	46,865,000		46,865,000		107,918,000
Securities owned	31,171,000		31,171,000		28,267,000
Available-for-sale debt securities
Schedule of Investments [Line Items]
Available-for-sale securities, gross realized losses			414,000	556,000
Investment Funds Sponsored by LSV
Schedule of Investments [Line Items]
Other long-term investments	6,000,000		6,000,000		$ 6,916,000
Unrealized gains (losses) on investments	$ (1,270,000)	$ 309,000	$ (916,000)	$ 766,000

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