Concentrations of Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Securities Purchased Under Agreements to Resell	$ 2,696	$ 10,645
Securities Sold Under Agreements to Repurchase	$ (25,075)	(30,027)
Investment Banking And Investment Management Receivables Collection Periods	90 days
Placement Fees Receivables Collection Period	180 days
Private Funds Capital Raising Receivables Collection 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	$ 309,075	184,993
Contract with Customer, Receivable, Net, Noncurrent	60,948	34,008
Bad Debt Expense	3,365	2,579	$ 2,261
Contract with Customer, Asset, Gross, Current	2,833	0
Contract with Customer, Asset, Gross, Noncurrent	541	0
Marketable Securities	$ 204,627	65,032
Percentage Of Marketable Securities Related To Corporate And Municipal Bonds And Other Debt Securities	73.00%
Percentage Of Marketable Securities Related To Equity Securities, Exchange Traded Funds And Mutual Funds	27.00%
Asset (Liability) Balance [Member]
Concentration Risk [Line Items]
Securities Purchased Under Agreements to Resell	$ 2,696	10,645
Securities Sold Under Agreements to Repurchase	(25,075)	(30,027)
Market Value of Collateral Received or (Pledged) [Member]
Concentration Risk [Line Items]
Securities Purchased Under Agreements to Resell	2,701	10,643
Securities Sold Under Agreements to Repurchase	$ (25,099)	$ (30,020)