Investments - Schedule of Available-for-Sale Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 1,047,364	$ 1,014,765
Gross Unrealized Gains	23,460	16,300
Gross Unrealized Losses	(7,334)	(13,587)
Fair Value	1,063,490	1,017,478
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	972,856	940,212
Gross Unrealized Gains	15,172	11,797
Gross Unrealized Losses	(5,895)	(10,932)
Fair Value	982,133	941,077
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	124,955	101,793
Gross Unrealized Gains	5,865	5,032
Gross Unrealized Losses	(432)	(984)
Fair Value	130,388	105,841
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	139,809	152,703
Gross Unrealized Gains	1,001	1,070
Gross Unrealized Losses	(2,327)	(2,975)
Fair Value	138,483	150,798
Corporate
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	398,049	379,727
Gross Unrealized Gains	7,017	4,382
Gross Unrealized Losses	(2,282)	(5,661)
Fair Value	402,784	378,448
Commercial mortgage and asset-backed
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	178,248	167,967
Gross Unrealized Gains	1,024	906
Gross Unrealized Losses	(523)	(826)
Fair Value	178,749	168,047
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	62,464	64,823
Gross Unrealized Gains	109	276
Gross Unrealized Losses	(141)	(85)
Fair Value	62,432	65,014
U.S. Treasury securities and obligations guaranteed by the U.S. government
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	67,306	71,174
Gross Unrealized Gains	93	131
Gross Unrealized Losses	(190)	(185)
Fair Value	67,209	71,120
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,025	2,025
Gross Unrealized Gains	63	0
Gross Unrealized Losses	0	(216)
Fair Value	2,088	1,809
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	74,508	74,553
Gross Unrealized Gains	8,288	4,503
Gross Unrealized Losses	(1,439)	(2,655)
Fair Value	$ 81,357	$ 76,401