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Investments (Number of Securities in an Unrealized Unrecognized Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Percentage Decline in Fair Value Percentage of Amortized Cost	1.00%	1.00%
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	$ 100	$ 0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	878,126	1,358,111
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4,961)	(15,651)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	35,686	15,626
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(397)	(406)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	913,812	1,373,737
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(5,358)	(16,057)
AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	869,566	1,340,672
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(4,664)	(14,991)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	35,686	15,626
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(397)	(406)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	905,252	1,356,298
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(5,061)	(15,397)
Equity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	8,560	17,439
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(297)	(660)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	8,560	17,439
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(297)	(660)
U.S. Government and Government Agencies [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	23,516	6,419
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(233)	(36)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	250	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	23,766	6,419
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(233)	(36)
Foreign Government [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,481	13,075
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(11)	(16)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	1,481	13,075
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(11)	(16)
Obligations of States and Political Subdivisions [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	107,514	306,509
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(422)	(5,304)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	14,139	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(160)	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	121,653	306,509
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(582)	(5,304)
Corporate Securities [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	238,326	462,902
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,744)	(5,771)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	3,228	4,913
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(18)	(89)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	241,554	467,815
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,762)	(5,860)
Collateralized Loan Obligations and Other Asset-Backed Securities [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	74,977	189,795
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(196)	(354)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,655	319
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(6)	(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	76,632	190,114
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(202)	(355)
Commercial Mortgage Backed Securities [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	154,267	82,492
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(773)	(1,021)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,214	1,645
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(68)	(7)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	159,481	84,137
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(841)	(1,028)
Residential Mortgage Backed Securities [Member] | AFS Fixed Maturity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	269,485	279,480
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(1,285)	(2,489)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	11,200	8,749
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	(145)	(309)
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	280,685	288,229
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(1,430)	(2,798)
Common Stock [Member] | Equity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	4,727	11,271
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(226)	(305)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	4,727	11,271
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	(226)	(305)
Nonredeemable Preferred Stock [Member] | Equity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	3,833	6,168
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(71)	(355)
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Total Fair Value	3,833	6,168
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ (71)	$ (355)

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- Definition

This item represents the percentage decline in fair value of fixed maturity securities compared to amortized cost that have been in a loss position for more than twelve months. This impairment has been determined to be temporary.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months.

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