Investments - Available-For-Sale Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fixed maturities, available-for-sale
Amortized Cost	$ 3,758,720	$ 3,852,411
Total Fair Value	3,493,597	3,472,472
U.S. Treasury obligations
Fixed maturities, available-for-sale
Amortized Cost	259,834	243,999
Due in one year or less	26,389
Due after one year through five years	181,056
Due after five years through ten years	33,387
Due after ten years	2,693
Total Fair Value	243,525	221,608
U.S. Government-sponsored enterprise obligations
Fixed maturities, available-for-sale
Amortized Cost	19,752	21,562
Due in one year or less	4,637
Due after one year through five years	13,574
Due after five years through ten years	513
Due after ten years	0
Total Fair Value	18,724	19,934
State and municipal bonds
Fixed maturities, available-for-sale
Amortized Cost	482,367	483,584
Due in one year or less	31,432
Due after one year through five years	153,891
Due after five years through ten years	156,855
Due after ten years	112,203
Total Fair Value	454,381	439,450
Corporate debt
Fixed maturities, available-for-sale
Amortized Cost	1,883,308	1,980,579
Due in one year or less	206,636
Due after one year through five years	885,777
Due after five years through ten years	573,432
Due after ten years	84,729
Total Fair Value	1,750,574	1,781,452
Residential mortgage-backed securities
Fixed maturities, available-for-sale
Amortized Cost	481,267	450,870
Total Fair Value	430,137	389,540
Agency commercial mortgage-backed securities
Fixed maturities, available-for-sale
Amortized Cost	9,369	10,576
Total Fair Value	8,387	9,704
Other commercial mortgage-backed securities
Fixed maturities, available-for-sale
Amortized Cost	210,469	217,021
Total Fair Value	189,474	194,090
Other asset-backed securities
Fixed maturities, available-for-sale
Amortized Cost	412,354	444,220
Total Fair Value	$ 398,395	$ 416,694