Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 418,312	$ 327,384	$ 1,299,057	$ 932,255
Management Fees	15,334	11,954	56,071	35,211
Incentive income	6	127	2,433	127
Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	418,087	327,151	1,298,362	931,536
Management Fees	15,109	11,721	55,376	34,492
Incentive income	6	127	2,433	127
Asset Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	225	233	695	719
Management Fees	225	233	695	719
Incentive income	0	0	0	0
Underwriting fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	91,108	121,390	334,092	318,355
Strategic/financial advisory fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	129,158	39,431	303,232	101,061
Placement and sales agent fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	49,561	28,427	153,485	71,999
Expense reimbursements from clients | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3,705	5,093	12,538	11,936
Investment banking revenue | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	273,532	194,341	803,347	503,351
Commissions | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	120,624	112,953	410,821	367,564
Trade conversion | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	3,707	3,404	11,685	12,370
Equity and credit research fees | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	5,109	4,605	14,700	13,632
Brokerage | Operating Company
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 129,440	$ 120,962	$ 437,206	$ 393,566