Corporate Borrowings - Indebtedness Outstanding (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total indebtedness outstanding	$ 249,410	$ 40,000
Less unamortized loan fees	(1,733)	(129)
Total indebtedness outstanding, net	247,677	39,871
Less current maturities of long-term debt	(3,227)	(1,600)
Long-term debt and Credit Agreement - Revolver	244,450	38,271
Other long-term borrowings
Debt Instrument [Line Items]
Total indebtedness outstanding	210	0
Credit Agreement - Revolver, 1.34% (variable rate) due 2025 | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Total indebtedness outstanding	$ 210,000	0
Credit agreement, interest rate (as a percent)	1.34%
Prudential Note Purchase Agreement, 3.53% (fixed rate) due 2027 | Secured Debt
Debt Instrument [Line Items]
Total indebtedness outstanding	$ 19,200	20,000
Senior secured notes, stated interest rate (as a percent)	3.53%
Prudential Note Purchase Agreement, 3.80% (fixed rate) due 2029 | Secured Debt
Debt Instrument [Line Items]
Total indebtedness outstanding	$ 20,000	$ 20,000
Senior secured notes, stated interest rate (as a percent)	3.80%