Investments - Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Marketable Securities
Estimated Fair Value, Less than 12 Months	$ 831,170	$ 369,954
Estimated Fair Value, 12 Months or More	263,554	13,488
Estimated Fair Value, Total	1,094,724	383,442
Unrealized Losses, Less than 12 Months	78,150	6,983
Unrealized Losses, 12 Months or More	48,456	591
Unrealized Losses, Total	126,606	7,574
Subtotal, fixed maturity securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	714,289	350,497
Estimated Fair Value, 12 Months or More	257,345	12,459
Estimated Fair Value, Total	971,634	362,956
Unrealized Losses, Less than 12 Months	56,952	5,424
Unrealized Losses, 12 Months or More	46,508	386
Unrealized Losses, Total	103,460	5,810
U.S. Treasury securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	1,669
Estimated Fair Value, Total	1,669
Unrealized Losses, Less than 12 Months	156
Unrealized Losses, Total	156
Obligations of states and political subdivisions
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	34,178	2,985
Estimated Fair Value, 12 Months or More	3,072	1,012
Estimated Fair Value, Total	37,250	3,997
Unrealized Losses, Less than 12 Months	2,504	85
Unrealized Losses, 12 Months or More	1,028	38
Unrealized Losses, Total	3,532	123
Residential mortgage-backed securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	140,855	97,116
Estimated Fair Value, 12 Months or More	70,956	11
Estimated Fair Value, Total	211,811	97,127
Unrealized Losses, Less than 12 Months	12,254	1,502
Unrealized Losses, 12 Months or More	13,507	1
Unrealized Losses, Total	25,761	1,503
Commercial mortgage-backed securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	110,073	29,660
Estimated Fair Value, 12 Months or More	24,653
Estimated Fair Value, Total	134,726	29,660
Unrealized Losses, Less than 12 Months	11,632	442
Unrealized Losses, 12 Months or More	4,847
Unrealized Losses, Total	16,479	442
Other asset-backed securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	41,113	39,266
Estimated Fair Value, 12 Months or More	27,618
Estimated Fair Value, Total	68,731	39,266
Unrealized Losses, Less than 12 Months	2,358	255
Unrealized Losses, 12 Months or More	3,071
Unrealized Losses, Total	5,429	255
Corporate and other securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	386,401	181,470
Estimated Fair Value, 12 Months or More	131,046	11,436
Estimated Fair Value, Total	517,447	192,906
Unrealized Losses, Less than 12 Months	28,048	3,140
Unrealized Losses, 12 Months or More	24,055	347
Unrealized Losses, Total	52,103	3,487
Equity securities
Equity Securities
Estimated Fair Value, Less than 12 Months	116,881	19,457
Estimated Fair Value, 12 Months or More	6,209	1,029
Estimated Fair Value, Total	123,090	20,486
Unrealized Losses, Less than 12 Months	21,198	1,559
Unrealized Losses, 12 Months or More	1,948	205
Unrealized Losses, Total	$ 23,146	$ 1,764