Fair Value - Fair Value Measurements on a Recurring Basis by Asset Class and Level of Input (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	$ 1,000,384
Fair value of loaned securities	6,125	$ 0
Available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,000,384	961,241
Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	612,049	588,688
Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	111,857	112,468
Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	123,013	102,720
Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	127,991	140,055
Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	24,449	17,310
U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,025
Fair Value, Measurements, Recurring Basis
Fair value measurements on a recurring basis by asset class and level of input
Total	1,080,512	1,045,494
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	1,000,384	961,241
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	612,049	588,688
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	111,857	112,468
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	123,013	102,720
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	127,991	140,055
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	24,449	17,310
Fair Value, Measurements, Recurring Basis | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,025
Fair Value, Measurements, Recurring Basis | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	80,128	84,253
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	65,321	69,900
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	5,543	5,810
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	3,689	3,901
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	3,885	3,915
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	1,500	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	190	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
Fair Value, Measurements, Recurring Basis | Level 1
Fair value measurements on a recurring basis by asset class and level of input
Total	1,537	863
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 | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	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	1,537	863
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	1,537	816
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	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	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
Fair Value, Measurements, Recurring Basis | Level 2
Fair value measurements on a recurring basis by asset class and level of input
Total	1,036,714	1,020,263
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	966,621	944,207
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	603,506	584,182
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	111,857	112,468
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	97,793	91,726
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	127,991	138,521
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	24,449	17,310
Fair Value, Measurements, Recurring Basis | Level 2 | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,025
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	70,093	76,056
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	58,350	63,750
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	5,543	5,810
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	3,689	3,901
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	2,321	2,415
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	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	190	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
Fair Value, Measurements, Recurring Basis | Level 3
Fair value measurements on a recurring basis by asset class and level of input
Total	42,261	24,368
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	33,763	17,034
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	8,543	4,506
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	25,220	10,994
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	0	1,534
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 | U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	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	8,498	7,334
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	5,434	5,334
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	1,564	1,500
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	1,500	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	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