Fair Value - Fair Value Measurements on a Recurring Basis by Asset Class and Level of Input (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	$ 1,387,147
Total	1,473,325	$ 1,455,591
Fair value of securities lent	55,300	64,500
Total available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,387,147	1,364,828
Fair value of securities lent	37,000	44,400
Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	861,267	844,479
Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	135,395	133,267
Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	144,118	140,541
Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	199,063	187,226
Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	35,820	35,152
U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	11,484	24,163
Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	86,178	90,763
Fair value of securities lent	18,300	20,100
Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	69,073	74,614
Equity securities | Utilities sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,662	3,696
Equity securities | Energy sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,011	2,713
Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	5,546	5,563
Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,470	3,224
Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	1,416	953
Level 1
Fair value measurements on a recurring basis by asset class and level of input
Total	3,518	3,591
Level 1 | Total available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,483	998
Level 1 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,483	998
Level 1 | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 1 | Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 1 | Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 1 | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 1 | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 1 | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	2,035	2,593
Level 1 | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	2,035	2,593
Level 1 | Equity securities | Utilities sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 1 | Equity securities | Energy sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 1 | Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 1 | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 1 | Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 2
Fair value measurements on a recurring basis by asset class and level of input
Total	1,430,142	1,412,181
Level 2 | Total available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,358,298	1,336,076
Level 2 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	856,026	839,542
Level 2 | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	135,395	133,267
Level 2 | Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	121,417	117,520
Level 2 | Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	198,156	186,432
Level 2 | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	35,820	35,152
Level 2 | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	11,484	24,163
Level 2 | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	71,844	76,105
Level 2 | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	61,376	66,350
Level 2 | Equity securities | Utilities sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,662	3,696
Level 2 | Equity securities | Energy sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,011	2,713
Level 2 | Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	2,379	2,393
Level 2 | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 2 | Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	1,416	953
Level 3
Fair value measurements on a recurring basis by asset class and level of input
Total	39,665	39,819
Level 3 | Total available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	27,366	27,754
Level 3 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	3,758	3,939
Level 3 | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 3 | Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	22,701	23,021
Level 3 | Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	907	794
Level 3 | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 3 | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Level 3 | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	12,299	12,065
Level 3 | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	5,662	5,671
Level 3 | Equity securities | Utilities sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 3 | Equity securities | Energy sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	0
Level 3 | Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,167	3,170
Level 3 | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,470	3,224
Level 3 | Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	$ 0	$ 0