Segment Operating Results - (Footnotes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Other Revenue, net	$ 25,315	$ 1,280	$ 68,832
Adjustments to Tax Receivable Agreements	0	0	77,535
Gain (Loss) on Disposition of Business	0	0	7,808
Net Realized And Unrealized Gains On Private Equity Fund Investments	(790)	(397)	(915)
Special Charges	10,141	5,012	25,437
Acquisition and Transition Costs	1,013	21	1,673
Total Other Expenses	36,865	30,387	47,965
Investment Banking [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	19,023	(3,156)	58,399
Interest expense on Notes Payable, Subordinated Borrowing and Line of Credit	12,917	9,201	9,960
Adjustments to Tax Receivable Agreements			77,535
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax			16,266
Amortization of LP Units/Interests and Certain Other Awards	18,183	15,241	11,444
Special Charges	7,202	5,012	14,400
Acquisition and Transition Costs	705	0	555
Fair Value of Contingent Consideration	0	1,485	0
Intangible Asset and Other Amortization	7,528	8,628	9,411
Total Other Expenses	33,618	30,366	35,810
Investment Management [Member]
Segment Reporting Information [Line Items]
Other Revenue, net	6,292	4,436	10,433
Gain (Loss) on Disposition of Business			7,808
Special Charges	2,939	0	11,037
Acquisition and Transition Costs	308	21	1,118
Total Other Expenses	$ 3,247	$ 21	12,155
Other Revenue, Including Interest and Investments [Member]
Segment Reporting Information [Line Items]
Principal Trading Gains (Losses)			(701)
Net Realized And Unrealized Gains On Private Equity Fund Investments			2,037
Other Revenue, Including Interest and Investments [Member] | Investment Banking [Member]
Segment Reporting Information [Line Items]
Principal Trading Gains (Losses)			(701)
Other Revenue, Including Interest and Investments [Member] | Investment Management [Member]
Segment Reporting Information [Line Items]
Net Realized And Unrealized Gains On Private Equity Fund Investments			$ 2,037