Fair Value Measurements - Summary of the Carrying Value and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Assets
Fixed maturity securities, available-for-sale	$ 1,597,695	$ 1,677,561
Bank loan participations	159,885	156,043
Cash and cash equivalents	350,740	190,123
Restricted cash equivalents	102,099	102,005	$ 723,525	$ 859,920
Short-term investments	130,435	136,563
Liabilities
Senior debt	222,300	262,300
Junior subordinated debt	104,055	104,055
Carrying Value
Assets
Fixed maturity securities, available-for-sale	1,597,695	1,677,561
Equity securities	98,653	108,410
Bank loan participations	159,885	156,043
Cash and cash equivalents	350,740	190,123
Restricted cash equivalents	102,099	102,005
Short-term investments	130,435	136,563
Other invested assets – notes receivable	9,740	9,740
Liabilities
Senior debt	222,300	262,300
Junior subordinated debt	104,055	104,055
Fair Value
Assets
Fixed maturity securities, available-for-sale	1,597,695	1,677,561
Equity securities	98,653	108,410
Bank loan participations	159,885	156,043
Cash and cash equivalents	350,740	190,123
Restricted cash equivalents	102,099	102,005
Short-term investments	130,435	136,563
Other invested assets – notes receivable	11,536	11,921
Liabilities
Senior debt	215,550	252,213
Junior subordinated debt	$ 108,235	$ 106,635