Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	$ 1,302,946	$ 1,199,409
Fixed maturity securities, available-for-sale	1,332,042	1,184,202
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	1,302,946	1,199,409
Total investments available-for-sale, Gross Unrealized Gains	32,213	6,060
Total investments available-for-sale, Gross Unrealized Losses	(3,117)	(21,267)
Fixed maturity securities, available-for-sale	1,332,042	1,184,202
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	130,215	147,160
Total investments available-for-sale, Gross Unrealized Gains	8,041	3,422
Total investments available-for-sale, Gross Unrealized Losses	(6)	(1,287)
Fixed maturity securities, available-for-sale	138,250	149,295
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	249,452	208,869
Total investments available-for-sale, Gross Unrealized Gains	2,212	577
Total investments available-for-sale, Gross Unrealized Losses	(1,906)	(5,337)
Fixed maturity securities, available-for-sale	249,758	204,109
Corporate
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	590,233	534,024
Total investments available-for-sale, Gross Unrealized Gains	16,672	1,516
Total investments available-for-sale, Gross Unrealized Losses	(631)	(10,772)
Fixed maturity securities, available-for-sale	606,274	524,768
Commercial mortgage and asset-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	216,771	199,528
Total investments available-for-sale, Gross Unrealized Gains	3,808	310
Total investments available-for-sale, Gross Unrealized Losses	(503)	(2,813)
Fixed maturity securities, available-for-sale	220,076	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	114,250	107,803
Total investments available-for-sale, Gross Unrealized Gains	1,454	235
Total investments available-for-sale, Gross Unrealized Losses	(71)	(845)
Fixed maturity securities, available-for-sale	115,633	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	26	0
Total investments available-for-sale, Gross Unrealized Losses	0	(213)
Fixed maturity securities, available-for-sale	$ 2,051	$ 1,812