Current Expected Credit Losses (CECL) - Schedule of Current Expected Credit Losses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 9,200	$ 2,800	$ 2,400	$ 2,600
Current-period provision for expected credit losses	5,800	(100)	12,600	100
Ending balance	15,000	2,700	15,000	2,700
Accrued commissions and other receivables, net
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,600	1,000	700	1,000
Current-period provision for expected credit losses	3,200	0	4,100	0
Ending balance	4,800	1,000	4,800	1,000
Loans, forgivable loans and other receivables from employees and partners, net
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,100	1,800	1,700	1,600
Current-period provision for expected credit losses	1,200	(100)	1,600	100
Ending balance	3,300	1,700	3,300	1,700
Receivables from broker-dealers, clearing organizations, customers and related broker-dealers
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	5,500	0	0	0
Current-period provision for expected credit losses	1,400	0	6,900	0
Ending balance	$ 6,900	$ 0	$ 6,900	$ 0