Significant Accounting Policies (Details) $ in Thousands		1 Months Ended	12 Months Ended
		Nov. 30, 2016	Dec. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Significant Accounting Policies [Line Items]
Total Assets			$ 3,370,888		$ 2,598,613	$ 2,125,667
Total Liabilities			1,881,514		1,472,363
Retained Earnings			$ (798,573)		(558,269)
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
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ (1,489,374)		(1,126,250)	(1,007,939)	$ (796,368)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2016-13 [Member]
Significant Accounting Policies [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]			$ 1,310
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
Retained Earnings [Member]
Significant Accounting Policies [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ (798,573)		(558,269)	$ (364,882)	$ (79,461)
Retained Earnings [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2016-13 [Member]
Significant Accounting Policies [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	[1]			$ 1,310
Variable Interest Entity, Primary Beneficiary [Member]
Significant Accounting Policies [Line Items]
Total Assets			377,878		227,885
Total Liabilities			$ 164,779		$ 129,494

[1] (2) The cumulative adjustment relates to the adoption of ASU No. 2016-13, "Measurement of Credit Losses on Financial Instruments" ("ASU 2016-13") on January 1, 2020, for which the Company recorded an adjustment to Retained Earnings to reflect the increase in the Company's Allowance for Doubtful Accounts as a result of the use of the current expected credit loss model. See Notes 2 and 3 for further information.