Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	$ 1,338,131	$ 1,199,409
Fixed maturity securities, available-for-sale	1,377,323	1,184,202
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	1,338,131	1,199,409
Total investments available-for-sale, Gross Unrealized Gains	40,955	6,060
Total investments available-for-sale, Gross Unrealized Losses	(1,763)	(21,267)
Fixed maturity securities, available-for-sale	1,377,323	1,184,202
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	145,016	147,160
Total investments available-for-sale, Gross Unrealized Gains	9,460	3,422
Total investments available-for-sale, Gross Unrealized Losses	(89)	(1,287)
Fixed maturity securities, available-for-sale	154,387	149,295
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	245,315	208,869
Total investments available-for-sale, Gross Unrealized Gains	2,849	577
Total investments available-for-sale, Gross Unrealized Losses	(951)	(5,337)
Fixed maturity securities, available-for-sale	247,213	204,109
Corporate
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	603,524	534,024
Total investments available-for-sale, Gross Unrealized Gains	21,887	1,516
Total investments available-for-sale, Gross Unrealized Losses	(231)	(10,772)
Fixed maturity securities, available-for-sale	625,180	524,768
Commercial mortgage and asset-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	230,417	199,528
Total investments available-for-sale, Gross Unrealized Gains	5,221	310
Total investments available-for-sale, Gross Unrealized Losses	(434)	(2,813)
Fixed maturity securities, available-for-sale	235,204	197,025
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	111,834	107,803
Total investments available-for-sale, Gross Unrealized Gains	1,538	235
Total investments available-for-sale, Gross Unrealized Losses	(40)	(845)
Fixed maturity securities, available-for-sale	113,332	107,193
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	0
Total investments available-for-sale, Gross Unrealized Losses	(18)	(213)
Fixed maturity securities, available-for-sale	$ 2,007	$ 1,812