Significant Accounting Policies (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2016	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
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
Contract Asset Recognized For Cost of Obtaining Contract With Benefit in Excess of Period		1 year
Other Operating Expenses		$ 42,020	$ 30,461	$ 23,442
Professional Fees		81,851	82,393	63,857
Net Realized And Unrealized Gains On Private Equity Fund Investments		(790)	(397)	(915)
Variable Interest Entity, Primary Beneficiary [Member]
Significant Accounting Policies [Line Items]
Consolidated Assets		227,885	190,223
Consolidated Liabilities		$ 129,494	$ 122,460
Execution, Clearing and Custody Fees [Member]
Significant Accounting Policies [Line Items]
Other Operating Expenses				13,572
Professional Fees				1,206
Other Revenue, Including Interest and Investments [Member]
Significant Accounting Policies [Line Items]
Principal Trading Losses				(701)
Net Realized And Unrealized Gains On Private Equity Fund Investments				$ 2,037
LP Units [Member]
Significant Accounting Policies [Line Items]
Limited Partnership Units Convertible Conversion Ratio	1	1
Minimum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		3 years
Award Vesting Period		1 year
Maximum [Member]
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		7 years
Award Vesting Period		5 years