Current Expected Credit Losses (CECL) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jan. 01, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Current expected credit losses reserve	$ 2,700		$ 2,700		$ 2,600	$ 1,900
Increase (decrease) in expected credit losses reserve	100	$ (400)	100	$ 900
Disposal Group, Held-for-sale, Not Discontinued Operations
Financing Receivable, Allowance for Credit Loss [Line Items]
Current expected credit losses reserve	100		100
Increase (decrease) in expected credit losses reserve			100
Accrued Commissions and Other Receivables, Net
Financing Receivable, Allowance for Credit Loss [Line Items]
Current expected credit losses reserve	1,200		1,200		1,000	800
Increase (decrease) in expected credit losses reserve	100	300	200	300
Accrued Commissions and Other Receivables, Net | Disposal Group, Held-for-sale, Not Discontinued Operations
Financing Receivable, Allowance for Credit Loss [Line Items]
Current expected credit losses reserve	100		100
Increase (decrease) in expected credit losses reserve			100
Loans, Forgivable Loans and Other Receivables from Employees and Partners, Net
Financing Receivable, Allowance for Credit Loss [Line Items]
Current expected credit losses reserve	1,500		1,500		$ 1,600	$ 1,100
Increase (decrease) in expected credit losses reserve	$ 0	$ (700)	$ 100	$ 600