Summary of Significant Accounting Policies (Net Cash Provided by Operating Activities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Accounting Policies [Abstract]
Net income	$ 107,015	$ 190,308
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	8,531	8,098
Amortization	9,424	16,887
Equity in earnings of unconsolidated affiliate	(28,879)	(32,459)
Distributions received from unconsolidated affiliate	29,219	32,961
Stock-based compensation	8,074	10,566
Provision for losses on receivables	(180)	(214)
Deferred income tax expense	(5,452)	(10,908)
Net (gain) loss from investments	(744)	489
Change in other long-term liabilities	938	1,138
Change in other assets	(783)	(706)
Contract costs capitalized, net of amortization	423	389
Other	123	1,228
Change in current assets and liabilities (Increase) decrease in
Receivables from investment products	6,270	1,452
Receivables	(962)	3,979
Other current assets	(2,261)	(2,556)
Advances due from unconsolidated affiliate	49,292	54,636
(Decrease) increase in
Accounts payable	877	(2,273)
Accrued liabilities	(65,998)	(18,078)
Deferred revenue	(563)	5,490
Total adjustments	7,349	70,119
Net cash provided by operating activities	$ 114,364	$ 260,427