Investments - Available-For-Sale Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fixed maturities, available-for-sale
Amortized Cost	$ 3,852,411	$ 3,814,847
Total Fair Value	3,472,472	3,833,722
U.S. Treasury obligations
Fixed maturities, available-for-sale
Amortized Cost	243,999	239,765
Due in one year or less	23,523
Due after one year through five years	139,958
Due after five years through ten years	56,909
Due after ten years	1,218
Total Fair Value	221,608	238,507
U.S. Government-sponsored enterprise obligations
Fixed maturities, available-for-sale
Amortized Cost	21,562	20,467
Due in one year or less	2,195
Due after one year through five years	13,790
Due after five years through ten years	3,949
Due after ten years	0
Total Fair Value	19,934	20,234
State and municipal bonds
Fixed maturities, available-for-sale
Amortized Cost	483,584	511,750
Due in one year or less	37,427
Due after one year through five years	144,161
Due after five years through ten years	151,294
Due after ten years	106,568
Total Fair Value	439,450	519,196
Corporate debt
Fixed maturities, available-for-sale
Amortized Cost	1,980,579	1,884,455
Due in one year or less	174,542
Due after one year through five years	854,788
Due after five years through ten years	654,558
Due after ten years	97,564
Total Fair Value	1,781,452	1,898,556
Residential mortgage-backed securities
Fixed maturities, available-for-sale
Amortized Cost	450,870	455,438
Total Fair Value	389,540	453,941
Agency commercial mortgage-backed securities
Fixed maturities, available-for-sale
Amortized Cost	10,576	13,909
Total Fair Value	9,704	14,141
Other commercial mortgage-backed securities
Fixed maturities, available-for-sale
Amortized Cost	217,021	231,226
Total Fair Value	194,090	231,483
Other asset-backed securities
Fixed maturities, available-for-sale
Amortized Cost	444,220	457,837
Total Fair Value	$ 416,694	$ 457,664