Investments - Fair Value and Gross Unrealized Losses (Details) $ in Thousands	Mar. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	$ 1,445,040
Fixed maturity securities, Fair Value, More than 12 Months	336,068
Fixed maturity securities, Fair Value, Total	1,781,108
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	118,815
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	42,739
Fixed maturity securities, Gross Unrealized Losses, Total	$ 161,554
Number of positions with a gross unrealized loss, 12 Months or Less \| security	1,080	330
Number of position with a gross unrealized loss, more than 12 months \| security	104	137
Number of position with a gross unrealized loss, Total \| security	1,184	467
Fair value as a percentage of total fixed maturities and equity securities fair value, 12 Months or Less	24.70%	8.30%
Fair value as a percentage of total fixed maturities and equity securities fair value, more than 12 months	5.80%	8.20%
Fair value as a percentage of total fixed maturities and equity securities fair value, Total	30.50%	16.50%
Mortgage-backed securities
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	$ 23,168	$ 72,422
Fixed maturity securities, Fair Value, More than 12 Months	1,003	2,620
Fixed maturity securities, Fair Value, Total	24,171	75,042
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	302	1,282
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	90	205
Fixed maturity securities, Gross Unrealized Losses, Total	392	1,487
Other
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	15,736	38,341
Fixed maturity securities, Fair Value, More than 12 Months	0	1,527
Fixed maturity securities, Fair Value, Total	15,736	39,868
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	60	619
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	0	2
Fixed maturity securities, Gross Unrealized Losses, Total	60	621
Municipal bonds
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	191,688	91,195
Fixed maturity securities, Fair Value, More than 12 Months	0	9,160
Fixed maturity securities, Fair Value, Total	191,688	100,355
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	7,376	977
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	0	603
Fixed maturity securities, Gross Unrealized Losses, Total	7,376	1,580
Foreign government bonds
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	13,225	0
Fixed maturity securities, Fair Value, More than 12 Months	0	0
Fixed maturity securities, Fair Value, Total	13,225	0
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	754	0
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	0	0
Fixed maturity securities, Gross Unrealized Losses, Total	754	0
Corporate bonds
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	549,628	58,198
Fixed maturity securities, Fair Value, More than 12 Months	5,761	16,622
Fixed maturity securities, Fair Value, Total	555,389	74,820
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	39,268	886
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	1,936	909
Fixed maturity securities, Gross Unrealized Losses, Total	41,204	1,795
Other mortgage-backed securities
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less	651,595	218,710
Fixed maturity securities, Fair Value, More than 12 Months	329,304	442,791
Fixed maturity securities, Fair Value, Total	980,899	661,501
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less	71,055	1,970
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months	40,713	6,161
Fixed maturity securities, Gross Unrealized Losses, Total	$ 111,768	8,131
Total Fixed Maturity Securities
Fixed maturity securities, Fair Value
Fixed maturity securities, Fair Value, 12 Months or Less		478,866
Fixed maturity securities, Fair Value, More than 12 Months		472,720
Fixed maturity securities, Fair Value, Total		951,586
Fixed maturity securities, Gross Unrealized Losses, 12 Months or Less		5,734
Fixed maturity securities, Gross Unrealized Losses, More than 12 Months		7,880
Fixed maturity securities, Gross Unrealized Losses, Total		$ 13,614

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