Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	$ 1,664,382
Fixed maturity securities, available-for-sale	1,747,404	$ 1,433,626
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	1,664,382	1,398,533
Total investments available-for-sale, Gross Unrealized Gains	86,157	37,691
Total investments available-for-sale, Gross Unrealized Losses	(3,135)	(2,598)
Fixed maturity securities, available-for-sale	1,747,404	1,433,626
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	254,226	159,894
Total investments available-for-sale, Gross Unrealized Gains	15,714	7,949
Total investments available-for-sale, Gross Unrealized Losses	(18)	(742)
Fixed maturity securities, available-for-sale	269,922	167,101
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	282,396	261,524
Total investments available-for-sale, Gross Unrealized Gains	8,853	3,244
Total investments available-for-sale, Gross Unrealized Losses	(61)	(622)
Fixed maturity securities, available-for-sale	291,188	264,146
Corporate
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	707,203	611,304
Total investments available-for-sale, Gross Unrealized Gains	47,479	21,306
Total investments available-for-sale, Gross Unrealized Losses	(240)	(389)
Fixed maturity securities, available-for-sale	754,442	632,221
Commercial mortgage and asset-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	303,161	249,309
Total investments available-for-sale, Gross Unrealized Gains	10,802	3,954
Total investments available-for-sale, Gross Unrealized Losses	(2,782)	(806)
Fixed maturity securities, available-for-sale	311,181	252,457
U.S. Treasury securities and obligations guaranteed by the U.S. government
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	115,371	114,477
Total investments available-for-sale, Gross Unrealized Gains	3,309	1,229
Total investments available-for-sale, Gross Unrealized Losses	0	(39)
Fixed maturity securities, available-for-sale	118,680	115,667
Redeemable preferred stock
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	2,025	2,025
Total investments available-for-sale, Gross Unrealized Gains	0	9
Total investments available-for-sale, Gross Unrealized Losses	(34)	0
Fixed maturity securities, available-for-sale	$ 1,991	$ 2,034