Investments (Investment Category and Duration of Gross Unrealized Losses on Fixed Maturity Securities and Equity Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	$ 91,761	$ 8,844
Gross unrealized losses on securities, less than 12 months, unrealized losses	(2,089)	(264)
Gross unrealized losses on securities, 12 months or more, fair value	13,804	24,980
Gross unrealized losses on securities, 12 months or more, unrealized losses	(996)	(1,830)
Gross unrealized losses on securities, fair value, total	105,565	33,824
Gross unrealized losses on securities, unrealized losses, total	(3,085)	(2,094)
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	1,375,697	720,465
Gross unrealized losses on securities, less than 12 months, unrealized losses	(62,930)	(13,740)
Gross unrealized losses on securities, 12 months or more, fair value	76,786	240,810
Gross unrealized losses on securities, 12 months or more, unrealized losses	(5,894)	(6,345)
Gross unrealized losses on securities, fair value, total	1,452,483	961,275
Gross unrealized losses on securities, unrealized losses, total	(68,824)	(20,085)
Fixed maturity securities | Corporate
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	1,093,249	640,641
Gross unrealized losses on securities, less than 12 months, unrealized losses	(60,491)	(13,132)
Gross unrealized losses on securities, 12 months or more, fair value	34,841	113,918
Gross unrealized losses on securities, 12 months or more, unrealized losses	(4,853)	(3,482)
Gross unrealized losses on securities, fair value, total	1,128,090	754,559
Gross unrealized losses on securities, unrealized losses, total	(65,344)	(16,614)
Fixed maturity securities | Commercial mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	1,137
Gross unrealized losses on securities, less than 12 months, unrealized losses	(1)
Gross unrealized losses on securities, 12 months or more, fair value	0
Gross unrealized losses on securities, 12 months or more, unrealized losses	0
Gross unrealized losses on securities, fair value, total	1,137
Gross unrealized losses on securities, unrealized losses, total	(1)
Fixed maturity securities | Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	215,948	22,337
Gross unrealized losses on securities, less than 12 months, unrealized losses	(1,714)	(71)
Gross unrealized losses on securities, 12 months or more, fair value	13,824	61,682
Gross unrealized losses on securities, 12 months or more, unrealized losses	(152)	(1,083)
Gross unrealized losses on securities, fair value, total	229,772	84,019
Gross unrealized losses on securities, unrealized losses, total	(1,866)	(1,154)
Common Stock | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	457	0
Gross unrealized losses on securities, less than 12 months, unrealized losses	(3)	0
Gross unrealized losses on securities, 12 months or more, fair value	0	196
Gross unrealized losses on securities, 12 months or more, unrealized losses	0	(1)
Gross unrealized losses on securities, fair value, total	457	196
Gross unrealized losses on securities, unrealized losses, total	(3)	(1)
Non-redeemable preferred stocks | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	91,304	8,844
Gross unrealized losses on securities, less than 12 months, unrealized losses	(2,086)	(264)
Gross unrealized losses on securities, 12 months or more, fair value	13,804	24,784
Gross unrealized losses on securities, 12 months or more, unrealized losses	(996)	(1,829)
Gross unrealized losses on securities, fair value, total	105,108	33,628
Gross unrealized losses on securities, unrealized losses, total	(3,082)	(2,093)
United States government and government agencies and authorities | Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	3,348	34,551
Gross unrealized losses on securities, less than 12 months, unrealized losses	(18)	(188)
Gross unrealized losses on securities, 12 months or more, fair value	5,859	21,488
Gross unrealized losses on securities, 12 months or more, unrealized losses	(5)	(241)
Gross unrealized losses on securities, fair value, total	9,207	56,039
Gross unrealized losses on securities, unrealized losses, total	(23)	(429)
States, municipalities and political subdivisions | Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	21,214	3,050
Gross unrealized losses on securities, less than 12 months, unrealized losses	(113)	(282)
Gross unrealized losses on securities, 12 months or more, fair value	0	4,633
Gross unrealized losses on securities, 12 months or more, unrealized losses	0	(71)
Gross unrealized losses on securities, fair value, total	21,214	7,683
Gross unrealized losses on securities, unrealized losses, total	(113)	(353)
Foreign governments | Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	40,801	19,886
Gross unrealized losses on securities, less than 12 months, unrealized losses	(593)	(67)
Gross unrealized losses on securities, 12 months or more, fair value	21,054	37,741
Gross unrealized losses on securities, 12 months or more, unrealized losses	(720)	(1,390)
Gross unrealized losses on securities, fair value, total	61,855	57,627
Gross unrealized losses on securities, unrealized losses, total	(1,313)	(1,457)
Asset-backed | Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	0	0
Gross unrealized losses on securities, less than 12 months, unrealized losses	0	0
Gross unrealized losses on securities, 12 months or more, fair value	1,208	1,348
Gross unrealized losses on securities, 12 months or more, unrealized losses	(164)	(78)
Gross unrealized losses on securities, fair value, total	1,208	1,348
Gross unrealized losses on securities, unrealized losses, total	$ (164)	$ (78)