Investments - Fair Value and Unrealized Losses (Details) $ in Thousands	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Fixed maturities, Fair value
Less than 12 Months, Fair value	$ 163,817	$ 123,780
12 Months or More, Fair value	147,131	262,519
Total, Fair value	310,948	386,299
Fixed maturities, Unrealized losses
Less than 12 months, Unrealized losses	(5,570)	(824)
12 months or more, Unrealized losses	(6,762)	(16,815)
Total, Unrealized losses	$ (12,332)	$ (17,639)
Number of securities in an unrealized loss position | security	116	104
Investments fair value	$ 310,948	$ 386,299
Investments, Continuous Unrealized Loss Position, Accumulated Loss	$ (12,332)	$ (17,639)
Number of securities in an unrealized loss position for 12 months or greater | security	54	67
Investments fair value, unrealized loss position for 12 months or greater	$ 147,131	$ 262,519
Investments in unrealized loss position for 12 months or greater, unrealized losses	(6,762)	(16,815)
U.S. agency bonds – mortgage-backed
Fixed maturities, Fair value
Less than 12 Months, Fair value	25,644	31,401
12 Months or More, Fair value	9,871	85,008
Total, Fair value	35,515	116,409
Fixed maturities, Unrealized losses
Less than 12 months, Unrealized losses	(252)	(257)
12 months or more, Unrealized losses	(109)	(1,034)
Total, Unrealized losses	(361)	(1,291)
Non-U.S. government and supranational bonds
Fixed maturities, Fair value
Less than 12 Months, Fair value	1,481	1,824
12 Months or More, Fair value	597	701
Total, Fair value	2,078	2,525
Fixed maturities, Unrealized losses
Less than 12 months, Unrealized losses	(11)	(22)
12 months or more, Unrealized losses	(21)	(69)
Total, Unrealized losses	(32)	(91)
Asset-backed securities
Fixed maturities, Fair value
Less than 12 Months, Fair value	35,748	60,863
12 Months or More, Fair value	60,211	17,594
Total, Fair value	95,959	78,457
Fixed maturities, Unrealized losses
Less than 12 months, Unrealized losses	(450)	(240)
12 months or more, Unrealized losses	(775)	(292)
Total, Unrealized losses	(1,225)	(532)
Corporate bonds
Fixed maturities, Fair value
Less than 12 Months, Fair value	100,944	29,692
12 Months or More, Fair value	76,452	159,216
Total, Fair value	177,396	188,908
Fixed maturities, Unrealized losses
Less than 12 months, Unrealized losses	(4,857)	(305)
12 months or more, Unrealized losses	(5,857)	(15,420)
Total, Unrealized losses	$ (10,714)	$ (15,725)