Investments Available-for-Sale Securities in a Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	$ 218,129	$ 89,168
Gross unrealized holding losses, less than 12 months	(2,690)	(558)
12 Months or Longer, Estimated Fair Value	104,063	125,043
12 Months or Longer, Gross Unrealized Holding Losses	(4,204)	(1,917)
Total Estimated Fair Value	322,192	214,211
Total Gross Unrealized Holding Losses	(6,894)	(2,475)
Total fixed maturities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value		78,389
Gross unrealized holding losses, less than 12 months		(327)
12 Months or Longer, Estimated Fair Value		125,043
12 Months or Longer, Gross Unrealized Holding Losses		(1,917)
Total Estimated Fair Value	322,200	203,432
Total Gross Unrealized Holding Losses	(6,900)	(2,244)
U.S. Treasury securities and obligations of U.S. government agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	0	3,497
Gross unrealized holding losses, less than 12 months	0	(2)
12 Months or Longer, Estimated Fair Value	495	5,488
12 Months or Longer, Gross Unrealized Holding Losses	(3)	(12)
Total Estimated Fair Value	495	8,985
Total Gross Unrealized Holding Losses	(3)	(14)
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	57,877	7,258
Gross unrealized holding losses, less than 12 months	(742)	(36)
12 Months or Longer, Estimated Fair Value	34,451	38,143
12 Months or Longer, Gross Unrealized Holding Losses	(1,128)	(376)
Total Estimated Fair Value	92,328	45,401
Total Gross Unrealized Holding Losses	(1,870)	(412)
Corporate and other securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	64,209	30,944
Gross unrealized holding losses, less than 12 months	(763)	(98)
12 Months or Longer, Estimated Fair Value	7,382	13,444
12 Months or Longer, Gross Unrealized Holding Losses	(122)	(74)
Total Estimated Fair Value	71,591	44,388
Total Gross Unrealized Holding Losses	(885)	(172)
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	73,520	27,609
Gross unrealized holding losses, less than 12 months	(823)	(108)
12 Months or Longer, Estimated Fair Value	9,511	10,706
12 Months or Longer, Gross Unrealized Holding Losses	(278)	(160)
Total Estimated Fair Value	83,031	38,315
Total Gross Unrealized Holding Losses	(1,101)	(268)
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value	22,523	9,081
Gross unrealized holding losses, less than 12 months	(362)	(83)
12 Months or Longer, Estimated Fair Value	52,224	57,262
12 Months or Longer, Gross Unrealized Holding Losses	(2,673)	(1,295)
Total Estimated Fair Value	74,747	66,343
Total Gross Unrealized Holding Losses	$ (3,035)	(1,378)
Total equity securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value		10,779
Gross unrealized holding losses, less than 12 months		(231)
12 Months or Longer, Estimated Fair Value		0
12 Months or Longer, Gross Unrealized Holding Losses		0
Total Estimated Fair Value		10,779
Total Gross Unrealized Holding Losses		(231)
Exchange traded funds [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value		130
Gross unrealized holding losses, less than 12 months		0
12 Months or Longer, Estimated Fair Value		0
12 Months or Longer, Gross Unrealized Holding Losses		0
Total Estimated Fair Value		130
Total Gross Unrealized Holding Losses		0
Nonredeemable preferred stock [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 Months, Estimated Fair Value		10,649
Gross unrealized holding losses, less than 12 months		(231)
12 Months or Longer, Estimated Fair Value		0
12 Months or Longer, Gross Unrealized Holding Losses		0
Total Estimated Fair Value		10,649
Total Gross Unrealized Holding Losses		$ (231)