Marketable Securities (Narrative) (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021	Dec. 31, 2021
Schedule of Investments [Line Items]
Cash equivalents at fair value	$ 474,736,000		$ 474,736,000		$ 422,838,000
Net unrealized loss	10,718,000		10,718,000		62,000
Net unrealized gains (losses) income tax expense (benefit)	(3,201,000)		(3,201,000)		(18,000)
Available-for-sale securities, gross realized gains			0	$ 0
Mutual funds and equities, gross realized gains			226,000	714,000
Mutual funds and equities, gross realized loss			714,000	65,000
Other long-term investments	39,012,000		39,012,000		107,918,000
Securities owned	31,586,000		31,586,000		28,267,000
Available-for-sale debt securities
Schedule of Investments [Line Items]
Available-for-sale securities, gross realized losses			521,000	861,000
Investment Funds Sponsored by LSV
Schedule of Investments [Line Items]
Other long-term investments	5,620,000		5,620,000		$ 6,916,000
Unrealized gains (losses) on investments	$ (380,000)	$ (39,000)	$ (1,296,000)	$ 727,000

Accumulated Other Comprehensive Income (Loss), Debt Securities, Available For Sale Securities Adjustment Tax

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Amount, after tax, of accumulated unrealized gain (loss) 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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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Amount of realized gain (loss) 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 of realized loss 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 of realized gain from sale of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

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Amount of long-term investments classified as other.

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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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Amount of unrealized gain (loss) on investment.

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