Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	$ 1,540,822	$ 1,398,533
Fixed maturity securities, available-for-sale	1,570,605	1,433,626
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	1,540,822	1,398,533
Total investments available-for-sale, Gross Unrealized Gains	44,434	37,691
Total investments available-for-sale, Gross Unrealized Losses	(14,651)	(2,598)
Fixed maturity securities, available-for-sale	1,570,605	1,433,626
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	173,919	159,894
Total investments available-for-sale, Gross Unrealized Gains	8,007	7,949
Total investments available-for-sale, Gross Unrealized Losses	(551)	(742)
Fixed maturity securities, available-for-sale	181,375	167,101
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	298,904	261,524
Total investments available-for-sale, Gross Unrealized Gains	9,366	3,244
Total investments available-for-sale, Gross Unrealized Losses	(831)	(622)
Fixed maturity securities, available-for-sale	307,439	264,146
Corporate
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	669,191	611,304
Total investments available-for-sale, Gross Unrealized Gains	19,583	21,306
Total investments available-for-sale, Gross Unrealized Losses	(3,753)	(389)
Fixed maturity securities, available-for-sale	685,021	632,221
Commercial mortgage and asset-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	274,448	249,309
Total investments available-for-sale, Gross Unrealized Gains	3,790	3,954
Total investments available-for-sale, Gross Unrealized Losses	(9,259)	(806)
Fixed maturity securities, available-for-sale	268,979	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	122,335	114,477
Total investments available-for-sale, Gross Unrealized Gains	3,688	1,229
Total investments available-for-sale, Gross Unrealized Losses	0	(39)
Fixed maturity securities, available-for-sale	126,023	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	(257)	0
Fixed maturity securities, available-for-sale	$ 1,768	$ 2,034