Fair Value Measurements - Summary of the Carrying Value and Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Assets
Fixed maturity securities, available-for-sale	$ 1,875,695	$ 1,783,417
Equity securities	118,116	118,627
Bank loan participations	143,762	154,991
Cash and cash equivalents	227,239	173,164
Restricted cash equivalents	105,502	103,215	$ 102,099	$ 102,005
Short-term investments	22,128	107,812
Liabilities
Senior debt	222,300	222,300
Junior subordinated debt	104,055	104,055
Carrying Value
Assets
Fixed maturity securities, available-for-sale	1,875,695	1,783,417
Equity securities	118,116	118,627
Bank loan participations	143,762	154,991
Cash and cash equivalents	227,239	173,164
Restricted cash equivalents	105,502	103,215
Short-term investments	22,128	107,812
Other invested assets – notes receivable	7,205	7,205
Liabilities
Senior debt	222,300	222,300
Junior subordinated debt	104,055	104,055
Fair Value
Assets
Fixed maturity securities, available-for-sale	1,875,695	1,783,417
Equity securities	118,116	118,627
Bank loan participations	143,762	154,991
Cash and cash equivalents	227,239	173,164
Restricted cash equivalents	105,502	103,215
Short-term investments	22,128	107,812
Other invested assets – notes receivable	7,676	7,703
Liabilities
Senior debt	228,409	226,063
Junior subordinated debt	$ 136,328	$ 127,149