Significant Accounting Policies (Details) $ in Thousands		1 Months Ended	12 Months Ended
		Nov. 30, 2016	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 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	[1]		$ 30,461	$ 23,442	$ 28,298
Professional Fees	[1]		82,393	63,857	56,401
Net Realized and Unrealized Gains on Private Equity Fund Investments			(397)	(915)	7,616
Variable Interest Entity, Primary Beneficiary [Member]
Significant Accounting Policies [Line Items]
Consolidated Assets			190,223	126,078
Consolidated Liabilities			$ 122,460	102,487
Execution, Clearing and Custody Fees [Member]
Significant Accounting Policies [Line Items]
Other Operating Expenses				13,572	16,278
Professional Fees				1,206	1,266
Other Revenue, Including Interest and Investments [Member]
Significant Accounting Policies [Line Items]
Principal Trading Losses				(701)	92
Net Realized and Unrealized Gains on Private Equity Fund Investments				$ 2,037	$ 12,403
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

[1] Certain balances in prior periods were reclassified to conform to their current presentation. See Note 2 for further information.