Fair Value - Fair Value Measurements on a Recurring Basis by Asset Class and Level of Input (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	$ 961,241
Available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	961,241	$ 894,661
Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	588,688	553,382
Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	112,468	102,537
Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	102,720	66,054
Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	140,055	150,415
Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	17,310	22,273
Fair Value, Measurements, Recurring Basis
Fair value measurements on a recurring basis by asset class and level of input
Total	1,045,494	967,221
Fair Value, Measurements, Recurring Basis | Available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	961,241	894,661
Fair Value, Measurements, Recurring Basis | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	588,688	553,382
Fair Value, Measurements, Recurring Basis | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	112,468	102,537
Fair Value, Measurements, Recurring Basis | Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	102,720	66,054
Fair Value, Measurements, Recurring Basis | Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	140,055	150,415
Fair Value, Measurements, Recurring Basis | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	17,310	22,273
Fair Value, Measurements, Recurring Basis | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	84,253	72,560
Fair Value, Measurements, Recurring Basis | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	69,900	61,084
Fair Value, Measurements, Recurring Basis | Equity securities | Utilities sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	5,810	5,708
Fair Value, Measurements, Recurring Basis | Equity securities | Energy sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,901	3,576
Fair Value, Measurements, Recurring Basis | Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,915	1,854
Fair Value, Measurements, Recurring Basis | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	500
Fair Value, Measurements, Recurring Basis | Equity securities | Industrial sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	180
Fair Value, Measurements, Recurring Basis | Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	47	338
Fair Value, Measurements, Recurring Basis | Level 1
Fair value measurements on a recurring basis by asset class and level of input
Total	863	0
Fair Value, Measurements, Recurring Basis | Level 1 | Available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Fair Value, Measurements, Recurring Basis | Level 1 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	0	0
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | Level 1 | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	863	0
Fair Value, Measurements, Recurring Basis | Level 1 | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	816	0
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | Level 1 | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0
Fair Value, Measurements, Recurring Basis | Level 1 | Equity securities | Industrial sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0
Fair Value, Measurements, Recurring Basis | Level 1 | Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	47	0
Fair Value, Measurements, Recurring Basis | Level 2
Fair value measurements on a recurring basis by asset class and level of input
Total	1,020,263	944,662
Fair Value, Measurements, Recurring Basis | Level 2 | Available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	944,207	875,881
Fair Value, Measurements, Recurring Basis | Level 2 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	584,182	549,696
Fair Value, Measurements, Recurring Basis | Level 2 | Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	112,468	102,537
Fair Value, Measurements, Recurring Basis | 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	91,726	55,144
Fair Value, Measurements, Recurring Basis | 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	138,521	146,231
Fair Value, Measurements, Recurring Basis | Level 2 | Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	17,310	22,273
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	76,056	68,781
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	63,750	57,305
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Utilities sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	5,810	5,708
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Energy sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	3,901	3,576
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	2,415	1,854
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Industrial sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	180
Fair Value, Measurements, Recurring Basis | Level 2 | Equity securities | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0	338
Fair Value, Measurements, Recurring Basis | Level 3
Fair value measurements on a recurring basis by asset class and level of input
Total	24,368	22,559
Fair Value, Measurements, Recurring Basis | Level 3 | Available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	17,034	18,780
Fair Value, Measurements, Recurring Basis | Level 3 | Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	4,506	3,686
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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	10,994	10,910
Fair Value, Measurements, Recurring Basis | 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	1,534	4,184
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | Level 3 | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	7,334	3,779
Fair Value, Measurements, Recurring Basis | Level 3 | Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	5,334	3,779
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | 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
Fair Value, Measurements, Recurring Basis | Level 3 | Equity securities | Consumer sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	1,500	0
Fair Value, Measurements, Recurring Basis | Level 3 | Equity securities | Technology sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	500
Fair Value, Measurements, Recurring Basis | Level 3 | Equity securities | Industrial sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	0
Fair Value, Measurements, Recurring Basis | 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