Fair Value Measurements - Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Apr. 24, 2020
Assets:
Total debt securities	$ 146,710	$ 151,999
Equity Securities	19,144	17,336
Short-term investments	10,142	13,317
Total marketable investments measured at fair value	175,996	182,652
Total assets measured at fair value	176,539	183,207
Liabilities:
Debt	34,486	40,997
Total Liabilities measured at fair value	36,974	40,036
Paycheck Protection Program
Liabilities:
Debt		2,745	$ 2,700
Line of credit
Liabilities:
Debt	1,000	5,000
U.S. Government
Assets:
Total debt securities	20,819	30,967
State and local government
Assets:
Total debt securities	31,417	33,265
Corporate debt
Assets:
Total debt securities	23,208	19,303
Asset-backed securities
Assets:
Total debt securities	30,980	20,963
Mortgage-backed securities
Assets:
Total debt securities	32,285	38,854
Commercial mortgage-backed securities
Assets:
Total debt securities	1,842	2,126
Collateralized mortgage obligations
Assets:
Total debt securities	6,159	6,521
Senior Unsecured Notes
Liabilities:
Debt	24,322	20,675
Subordinated notes
Liabilities:
Debt	11,652	11,616
Level 1
Assets:
Total debt securities	0	0
Equity Securities	18,861	17,053
Short-term investments	10,142	13,317
Total marketable investments measured at fair value	29,003	30,370
Liabilities:
Total Liabilities measured at fair value	0	0
Level 1 | U.S. Government
Assets:
Total debt securities	0	0
Level 1 | State and local government
Assets:
Total debt securities	0	0
Level 1 | Corporate debt
Assets:
Total debt securities	0	0
Level 1 | Asset-backed securities
Assets:
Total debt securities	0	0
Level 1 | Mortgage-backed securities
Assets:
Total debt securities	0	0
Level 1 | Commercial mortgage-backed securities
Assets:
Total debt securities	0	0
Level 1 | Collateralized mortgage obligations
Assets:
Total debt securities	0	0
Level 1 | Senior Unsecured Notes
Liabilities:
Debt	0	0
Level 1 | Subordinated notes
Liabilities:
Debt	0	0
Level 2
Assets:
Total debt securities	146,710	151,999
Equity Securities	283	283
Short-term investments	0	0
Total marketable investments measured at fair value	146,993	152,282
Liabilities:
Total Liabilities measured at fair value	25,322	28,420
Level 2 | Paycheck Protection Program
Liabilities:
Debt		2,745
Level 2 | Line of credit
Liabilities:
Debt	1,000	5,000
Level 2 | U.S. Government
Assets:
Total debt securities	20,819	30,967
Level 2 | State and local government
Assets:
Total debt securities	31,417	33,265
Level 2 | Corporate debt
Assets:
Total debt securities	23,208	19,303
Level 2 | Asset-backed securities
Assets:
Total debt securities	30,980	20,963
Level 2 | Mortgage-backed securities
Assets:
Total debt securities	32,285	38,854
Level 2 | Commercial mortgage-backed securities
Assets:
Total debt securities	1,842	2,126
Level 2 | Collateralized mortgage obligations
Assets:
Total debt securities	6,159	6,521
Level 2 | Senior Unsecured Notes
Liabilities:
Debt	24,322	20,675
Level 2 | Subordinated notes
Liabilities:
Debt		0
Level 3
Assets:
Total debt securities	0	0
Equity Securities	0	0
Short-term investments	0	0
Total marketable investments measured at fair value	0	0
Liabilities:
Total Liabilities measured at fair value	11,652	11,616
Level 3 | U.S. Government
Assets:
Total debt securities	0	0
Level 3 | State and local government
Assets:
Total debt securities	0	0
Level 3 | Corporate debt
Assets:
Total debt securities	0	0
Level 3 | Asset-backed securities
Assets:
Total debt securities	0	0
Level 3 | Mortgage-backed securities
Assets:
Total debt securities	0	0
Level 3 | Commercial mortgage-backed securities
Assets:
Total debt securities	0	0
Level 3 | Collateralized mortgage obligations
Assets:
Total debt securities	0	0
Level 3 | Senior Unsecured Notes
Liabilities:
Debt	0	0
Level 3 | Subordinated notes
Liabilities:
Debt	11,652	11,616
Partnership interest
Assets:
Investments measured at NAV	$ 543	$ 555