Fair Value - Fair Value Measurements on a Recurring Basis by Asset Class and Level of Input (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	$ 1,112,707
Fair value of securities lent	12,300
Total available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,112,707	$ 1,043,615
Corporate debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	695,332	643,943
Fair value of securities lent	12,200	7,300
Collateralized debt obligations
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	107,465	114,127
Commercial mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	120,026	124,982
Residential mortgage-backed securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	144,479	133,812
Other debt securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	36,270	26,751
U.S. Treasury
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	9,135
Equity securities | Financial services sector
Fair value measurements on a recurring basis by asset class and level of input
Fair value of securities lent	100
Fair Value, Measurements, Recurring Basis
Fair value measurements on a recurring basis by asset class and level of input
Total	1,194,619	1,129,506
Fair Value, Measurements, Recurring Basis | Total available-for-sale securities
Fair value measurements on a recurring basis by asset class and level of input
Total available-for-sale securities	1,112,707	1,043,615
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	695,332	643,943
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	107,465	114,127
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	120,026	124,982
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	144,479	133,812
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	36,270	26,751
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	9,135
Fair Value, Measurements, Recurring Basis | Equity securities
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	81,912	85,891
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	67,776	69,930
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	4,229	5,629
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	2,995	4,117
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	4,037	3,341
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	1,974	1,974
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	901	900
Fair Value, Measurements, Recurring Basis | Level 1
Fair value measurements on a recurring basis by asset class and level of input
Total	1,030	1,106
Fair Value, Measurements, Recurring Basis | 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	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	1,030	1,106
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	1,001	1,052
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	29	54
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 | Communications 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
Fair value measurements on a recurring basis by asset class and level of input
Total	1,168,165	1,091,069
Fair Value, Measurements, Recurring Basis | 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	1,095,930	1,013,258
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	689,302	637,675
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	106,770	114,127
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	110,897	100,893
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	143,556	133,812
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	36,270	26,751
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	9,135
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	72,235	77,811
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	63,263	65,378
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	4,229	5,629
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	2,995	4,117
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	847	1,787
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 | Communications sector
Fair value measurements on a recurring basis by asset class and level of input
Total equity securities	901	900
Fair Value, Measurements, Recurring Basis | Level 3
Fair value measurements on a recurring basis by asset class and level of input
Total	25,424	37,331
Fair Value, Measurements, Recurring Basis | 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	16,777	30,357
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	6,030	6,268
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	695	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	9,129	24,089
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	923	0
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	8,647	6,974
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	3,512	3,500
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	3,161	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	1,974	1,974
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