Corporate Borrowings - Indebtedness Outstanding (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Long-term debt, gross	$ 40,000	$ 40,000
Less unamortized loan fees	(124)	(129)
Total indebtedness outstanding, net	39,876	39,871
Less current maturities of long-term debt	(2,400)	(1,600)
Long-term debt and Credit Agreement - Revolver	37,476	38,271
Credit Agreement - Revolver, 1.12% (variable rate) due 2025 \| Line of Credit \| Revolving Credit Facility
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	0
Credit agreement, interest rate (as a percent)	1.12%
Prudential Note Purchase Agreement, 3.53% (fixed rate) due 2027 \| Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 20,000	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]
Long-term debt, gross	$ 20,000	$ 20,000
Senior secured notes, stated interest rate (as a percent)	3.80%

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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