Investments - Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Marketable Securities
Estimated Fair Value, Less than 12 Months	$ 1,032,722	$ 369,954
Estimated Fair Value, 12 Months or More	77,106	13,488
Estimated Fair Value, Total	1,109,828	383,442
Unrealized Losses, Less than 12 Months	92,375	6,983
Unrealized Losses, 12 Months or More	9,222	591
Unrealized Losses, Total	101,597	7,574
Subtotal, fixed maturity securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	911,653	350,497
Estimated Fair Value, 12 Months or More	52,693	12,459
Estimated Fair Value, Total	964,346	362,956
Unrealized Losses, Less than 12 Months	72,186	5,424
Unrealized Losses, 12 Months or More	7,938	386
Unrealized Losses, Total	80,124	5,810
U.S. Treasury securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	1,720
Estimated Fair Value, Total	1,720
Unrealized Losses, Less than 12 Months	106
Unrealized Losses, Total	106
Obligations of states and political subdivisions
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	37,017	2,985
Estimated Fair Value, 12 Months or More	827	1,012
Estimated Fair Value, Total	37,844	3,997
Unrealized Losses, Less than 12 Months	2,541	85
Unrealized Losses, 12 Months or More	223	38
Unrealized Losses, Total	2,764	123
Residential mortgage-backed securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	189,293	97,116
Estimated Fair Value, 12 Months or More	13,025	11
Estimated Fair Value, Total	202,318	97,127
Unrealized Losses, Less than 12 Months	15,210	1,502
Unrealized Losses, 12 Months or More	1,961	1
Unrealized Losses, Total	17,171	1,503
Commercial mortgage-backed securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	142,502	29,660
Estimated Fair Value, 12 Months or More	5,040
Estimated Fair Value, Total	147,542	29,660
Unrealized Losses, Less than 12 Months	9,319	442
Unrealized Losses, 12 Months or More	1,009
Unrealized Losses, Total	10,328	442
Other asset-backed securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	69,613	39,266
Estimated Fair Value, 12 Months or More	288
Estimated Fair Value, Total	69,901	39,266
Unrealized Losses, Less than 12 Months	4,111	255
Unrealized Losses, 12 Months or More	16
Unrealized Losses, Total	4,127	255
Corporate and other securities
Fixed Maturity Securities
Estimated Fair Value, Less than 12 Months	471,508	181,470
Estimated Fair Value, 12 Months or More	33,513	11,436
Estimated Fair Value, Total	505,021	192,906
Unrealized Losses, Less than 12 Months	40,899	3,140
Unrealized Losses, 12 Months or More	4,729	347
Unrealized Losses, Total	45,628	3,487
Equity securities
Equity Securities
Estimated Fair Value, Less than 12 Months	121,069	19,457
Estimated Fair Value, 12 Months or More	22,637	1,029
Estimated Fair Value, Total	143,706	20,486
Unrealized Losses, Less than 12 Months	20,189	1,559
Unrealized Losses, 12 Months or More	1,284	205
Unrealized Losses, Total	$ 21,473	$ 1,764