Concentrations of Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Risks and Uncertainties [Abstract]
Investment Banking And Investment Management Receivables Collection Periods	90 days
Placement Fees Receivables Collection Period	180 days
Contract Asset Recognized For Cost of Obtaining Contract With Benefit in Excess of Period	1 year
Collection Period For Restructuring Transactions	90 days
Receivables Reflected in Other Assets in Excess of Period	1 year
Accounts Receivable, Net of Allowance	$ 368,346	$ 296,355
Contract with Customer, Receivable, Net, Noncurrent	70,975	63,554	$ 60,948
Bad Debt Expense	6,878	10,451	3,365
Contract with Customer, Asset, Gross, Current	29,327	31,525	2,833
Contract with Customer, Asset, Gross, Noncurrent	5,283	2,504	$ 541
Investment Securities	$ 1,060,836	$ 409,150
Percentage Of Marketable Securities Related To Corporate And Municipal Bonds And Other Debt Securities	90.00%
Percentage Of Marketable Securities Related To Equity Securities, Exchange Traded Funds And Mutual Funds	10.00%