Income Taxes Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Operating Loss Carryforwards	$ 18,039	$ 60,160
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	24,068	46,545
Deferred Tax Liabilities, Intangible Assets	4,513	2,969
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	6,230	6,716
Deferred Tax Assets, Acquired Lease Liability	20,401	24,623
Deferred Tax Assets, Other	2,858	3,043
Deferred Tax Liabilities, Deferred Expense	1,686	3,980
Deferred Tax Assets, Gross	76,109	144,056
Deferred Tax Assets, Valuation Allowance	(5,194)	(5,234)
Deferred Tax Assets, Net of Valuation Allowance	70,915	138,822
Deferred Tax Liabilities, Investments	19,443	23,028
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	33,439	26,545
Deferred Tax Liabilities, Other	7,317	6,103
Deferred Tax Liabilities, Gross	(61,885)	(59,656)
Deferred Income Tax Expense (Benefit)	70,118	13,296	$ 18,965
Deferred tax assets/(liabilities), net	$ 9,030	$ 79,166