Investments - Schedule of Gross Unrealized Losses and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	$ 378,695	$ 492,187
Less Than 12 Months, Gross Unrealized Losses	(2,796)	(9,100)
12 Months or More, Fair Value	90,310	54,560
12 Months or More, Gross Unrealized Losses	(3,806)	(4,487)
Total, Fair Value	469,005	546,747
Total, Gross Unrealized Losses	(6,602)	(13,587)
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	374,782	470,842
Less Than 12 Months, Gross Unrealized Losses	(2,728)	(8,029)
12 Months or More, Fair Value	81,463	48,002
12 Months or More, Gross Unrealized Losses	(2,361)	(2,903)
Total, Fair Value	456,245	518,844
Total, Gross Unrealized Losses	(5,089)	(10,932)
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	27,813	28,398
Less Than 12 Months, Gross Unrealized Losses	(220)	(984)
12 Months or More, Fair Value	5,371	0
12 Months or More, Gross Unrealized Losses	(196)	0
Total, Fair Value	33,184	28,398
Total, Gross Unrealized Losses	(416)	(984)
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	81,667	93,242
Less Than 12 Months, Gross Unrealized Losses	(882)	(1,548)
12 Months or More, Fair Value	30,486	32,330
12 Months or More, Gross Unrealized Losses	(1,060)	(1,427)
Total, Fair Value	112,153	125,572
Total, Gross Unrealized Losses	(1,942)	(2,975)
Corporate
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	106,427	199,841
Less Than 12 Months, Gross Unrealized Losses	(998)	(4,212)
12 Months or More, Fair Value	31,522	8,477
12 Months or More, Gross Unrealized Losses	(903)	(1,449)
Total, Fair Value	137,949	208,318
Total, Gross Unrealized Losses	(1,901)	(5,661)
Commercial mortgage and asset-backed
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	46,526	47,990
Less Than 12 Months, Gross Unrealized Losses	(288)	(799)
12 Months or More, Fair Value	11,861	7,195
12 Months or More, Gross Unrealized Losses	(201)	(27)
Total, Fair Value	58,387	55,185
Total, Gross Unrealized Losses	(489)	(826)
Obligations of U.S. government corporations and agencies
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	52,157	50,573
Less Than 12 Months, Gross Unrealized Losses	(97)	(85)
12 Months or More, Fair Value	0	0
12 Months or More, Gross Unrealized Losses	0	0
Total, Fair Value	52,157	50,573
Total, Gross Unrealized Losses	(97)	(85)
U.S. Treasury securities and obligations guaranteed by the U.S. government
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	60,192	48,989
Less Than 12 Months, Gross Unrealized Losses	(243)	(185)
12 Months or More, Fair Value	2,223	0
12 Months or More, Gross Unrealized Losses	(1)	0
Total, Fair Value	62,415	48,989
Total, Gross Unrealized Losses	(244)	(185)
Redeemable preferred stock
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value		1,809
Less Than 12 Months, Gross Unrealized Losses		(216)
12 Months or More, Fair Value		0
12 Months or More, Gross Unrealized Losses		0
Total, Fair Value		1,809
Total, Gross Unrealized Losses		(216)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Less Than 12 Months, Fair Value	3,913	21,345
Less Than 12 Months, Gross Unrealized Losses	(68)	(1,071)
12 Months or More, Fair Value	8,847	6,558
12 Months or More, Gross Unrealized Losses	(1,445)	(1,584)
Total, Fair Value	12,760	27,903
Total, Gross Unrealized Losses	$ (1,513)	$ (2,655)