Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	$ 1,039,778	$ 1,008,662
Total investments available-for-sale, Fair Value	1,021,387	1,016,098
Equity securities, Cost or Amortized Cost	77,995	75,318
Equity securities, Gross Unrealized Gains	6,675	7,830
Equity securities, Gross Unrealized Loss	(661)	(626)
Equity securities, Fair Value	84,009	82,522
Total investments available-for-sale, Cost or Amortized Cost	1,117,773	1,083,980
Total investments available-for-sale, Gross Unrealized Gains	12,476	22,394
Total investments available-for-sale, Gross Unrealized Losses	(24,853)	(7,754)
Total investments available-for-sale, Fair Value	1,105,396	1,098,620
Fixed maturity securities
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	1,039,778	1,008,662
Total investments available-for-sale, Gross Unrealized Gains	5,801	14,564
Total investments available-for-sale, Gross Unrealized Losses	(24,192)	(7,128)
Total investments available-for-sale, Fair Value	1,021,387	1,016,098
State and municipal
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	137,055	139,382
Total investments available-for-sale, Gross Unrealized Gains	3,590	5,587
Total investments available-for-sale, Gross Unrealized Losses	(2,272)	(603)
Total investments available-for-sale, Fair Value	138,373	144,366
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	190,574	160,379
Total investments available-for-sale, Gross Unrealized Gains	445	723
Total investments available-for-sale, Gross Unrealized Losses	(6,268)	(2,441)
Total investments available-for-sale, Fair Value	184,751	158,661
Corporate
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	439,993	408,857
Total investments available-for-sale, Gross Unrealized Gains	1,655	7,503
Total investments available-for-sale, Gross Unrealized Losses	(11,303)	(2,639)
Total investments available-for-sale, Fair Value	430,345	413,721
Commercial mortgage and asset-backed
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	177,286	182,595
Total investments available-for-sale, Gross Unrealized Gains	85	714
Total investments available-for-sale, Gross Unrealized Losses	(2,929)	(698)
Total investments available-for-sale, Fair Value	174,442	182,611
Obligations of U.S. government corporations and agencies
Debt Securities, Available-for-sale [Line Items]
Total fixed maturity securities, Cost or Amortized Cost	5,702	35,948
Total investments available-for-sale, Gross Unrealized Gains	0	0
Total investments available-for-sale, Gross Unrealized Losses	(13)	(101)
Total investments available-for-sale, Fair Value	5,689	35,847
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	87,143	79,476
Total investments available-for-sale, Gross Unrealized Gains	26	37
Total investments available-for-sale, Gross Unrealized Losses	(1,372)	(639)
Total investments available-for-sale, Fair Value	85,797	78,874
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	(35)	(7)
Total investments available-for-sale, Fair Value	$ 1,990	$ 2,018