Concentrations of Credit Risk Concentrations of Credit Risk (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Concentration Risk [Line Items]
Securities Purchased Under Agreements to Resell	$ 13,566	$ 2,696
Securities Sold Under Agreements to Repurchase	$ 26,000	25,075
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	$ 296,355	309,075
Contract with Customer, Receivable, Net, Noncurrent	63,554	60,948	$ 34,008
Bad Debt Expense	10,451	3,365	2,579
Contract with Customer, Asset, Gross, Current	31,525	2,833	0
Contract with Customer, Asset, Gross, Noncurrent	2,504	541	$ 0
Investment Securities	$ 409,150	204,627
Percentage Of Marketable Securities Related To Corporate And Municipal Bonds And Other Debt Securities	84.00%
Percentage Of Marketable Securities Related To Equity Securities, Exchange Traded Funds And Mutual Funds	16.00%
Asset (Liability) Balance [Member]
Concentration Risk [Line Items]
Securities Purchased Under Agreements to Resell	$ 13,566	2,696
Securities Sold Under Agreements to Repurchase	26,000	25,075
Market Value of Collateral Received or (Pledged) [Member]
Concentration Risk [Line Items]
Securities Purchased Under Agreements to Resell	13,572	2,701
Securities Sold Under Agreements to Repurchase	$ 25,992	$ 25,099