Investments Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities
Estimated Fair Value, Less than 12 Months	$ 359,447	$ 154,847
Estimated Fair Value, 12 Months or More	27,064	60,844
Estimated Fair Value, Total	386,511	215,691
Unrealized Losses, Less than 12 Months	38,008	1,742
Unrealized Losses, 12 Months or More	5,956	2,259
Unrealized Losses, Total	43,964	4,001
Fixed maturity securities
Marketable Securities
Estimated Fair Value, Less than 12 Months	291,803	145,998
Estimated Fair Value, 12 Months or More	17,155	46,701
Estimated Fair Value, Total	308,958	192,699
Unrealized Losses, Less than 12 Months	24,017	1,351
Unrealized Losses, 12 Months or More	2,602	1,287
Unrealized Losses, Total	26,619	2,638
Obligations of states and political subdivisions
Marketable Securities
Estimated Fair Value, Less than 12 Months	656
Estimated Fair Value, Total	656
Unrealized Losses, Less than 12 Months	34
Unrealized Losses, Total	34
Residential mortgage-backed securities
Marketable Securities
Estimated Fair Value, Less than 12 Months	20,492	61,933
Estimated Fair Value, 12 Months or More	195	31,655
Estimated Fair Value, Total	20,687	93,588
Unrealized Losses, Less than 12 Months	99	409
Unrealized Losses, 12 Months or More	4	500
Unrealized Losses, Total	103	909
Commercial mortgage-backed securities
Marketable Securities
Estimated Fair Value, Less than 12 Months	22,272	36,398
Estimated Fair Value, 12 Months or More		866
Estimated Fair Value, Total	22,272	37,264
Unrealized Losses, Less than 12 Months	165	397
Unrealized Losses, Total	165	397
Other asset-backed securities
Marketable Securities
Estimated Fair Value, Less than 12 Months	14,840	21,281
Estimated Fair Value, 12 Months or More	8,202	462
Estimated Fair Value, Total	23,042	21,743
Unrealized Losses, Less than 12 Months	534	64
Unrealized Losses, 12 Months or More	881
Unrealized Losses, Total	1,415	64
Corporate and other securities
Marketable Securities
Estimated Fair Value, Less than 12 Months	233,543	26,386
Estimated Fair Value, 12 Months or More	8,758	13,718
Estimated Fair Value, Total	242,301	40,104
Unrealized Losses, Less than 12 Months	23,185	481
Unrealized Losses, 12 Months or More	1,717	787
Unrealized Losses, Total	24,902	1,268
Equity securities
Equity Securities
Estimated Fair Value, Less than 12 Months	67,644	8,849
Estimated Fair Value, 12 Months or More	9,909	14,143
Estimated Fair Value, Total	77,553	22,992
Unrealized Losses, Less than 12 Months	13,991	391
Unrealized Losses, 12 Months or More	3,354	972
Unrealized Losses, Total	$ 17,345	$ 1,363