Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 327,384	$ 175,943	$ 932,255	$ 583,682
Management Fees	11,954	7,300	35,211	21,480
Incentive income	127	701	127	724
Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	327,151	175,695	931,536	582,680
Management Fees	11,721	7,052	34,492	20,492
Incentive income	127	701	127	710
Asset Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	233	248	719	1,002
Management Fees	233	248	719	988
Incentive income	0	0	0	14
Underwriting fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	121,390	38,936	318,355	162,140
Strategic/financial advisory fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	39,431	17,889	101,061	49,565
Placement and sales agent fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	28,427	15,842	71,999	48,855
Expense reimbursements from clients | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	5,093	4,625	11,936	11,543
Investment banking revenue | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	194,341	77,292	503,351	272,103
Commissions | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	112,953	82,715	367,564	263,831
Trade conversion | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3,404	3,700	12,370	12,364
Equity and credit research fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,605	4,235	13,632	13,180
Brokerage | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 120,962	$ 90,650	$ 393,566	$ 289,375