Investments (Investment Category and Duration of Gross Unrealized Losses on Fixed Maturity Securities and Equity Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fixed maturity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	$ 769,984	$ 2,018,037
Gross unrealized losses on securities, less than 12 months, unrealized losses	(44,666)	(89,332)
Gross unrealized losses on securities, 12 months or more, fair value	146,404	94,115
Gross unrealized losses on securities, 12 months or more, unrealized losses	(12,809)	(11,547)
Gross unrealized losses on securities, fair value, total	916,388	2,112,152
Gross unrealized losses on securities, unrealized losses, total	(57,475)	(100,879)
Fixed maturity securities | United States government and government agencies and authorities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	19,565	90,008
Gross unrealized losses on securities, less than 12 months, unrealized losses	(5)	(465)
Gross unrealized losses on securities, 12 months or more, fair value	0	5,564
Gross unrealized losses on securities, 12 months or more, unrealized losses	0	(72)
Gross unrealized losses on securities, fair value, total	19,565	95,572
Gross unrealized losses on securities, unrealized losses, total	(5)	(537)
Fixed maturity securities | States, municipalities and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value		6,881
Gross unrealized losses on securities, less than 12 months, unrealized losses		(94)
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		6,881
Gross unrealized losses on securities, unrealized losses, total		(94)
Fixed maturity securities | Foreign governments
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	23,005	24,071
Gross unrealized losses on securities, less than 12 months, unrealized losses	(28)	(347)
Gross unrealized losses on securities, 12 months or more, fair value	24,700	22,239
Gross unrealized losses on securities, 12 months or more, unrealized losses	(437)	(376)
Gross unrealized losses on securities, fair value, total	47,705	46,310
Gross unrealized losses on securities, unrealized losses, total	(465)	(723)
Fixed maturity securities | Asset-backed
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	995	1,136
Gross unrealized losses on securities, 12 months or more, unrealized losses	(306)	(204)
Gross unrealized losses on securities, fair value, total	995	1,136
Gross unrealized losses on securities, unrealized losses, total	(306)	(204)
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	63,375	260,620
Gross unrealized losses on securities, less than 12 months, unrealized losses	(193)	(3,179)
Gross unrealized losses on securities, 12 months or more, fair value	17,348	11,147
Gross unrealized losses on securities, 12 months or more, unrealized losses	(103)	(230)
Gross unrealized losses on securities, fair value, total	80,723	271,767
Gross unrealized losses on securities, unrealized losses, total	(296)	(3,409)
Fixed maturity securities | Corporate
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	664,039	1,636,457
Gross unrealized losses on securities, less than 12 months, unrealized losses	(44,440)	(85,247)
Gross unrealized losses on securities, 12 months or more, fair value	103,361	54,029
Gross unrealized losses on securities, 12 months or more, unrealized losses	(11,963)	(10,665)
Gross unrealized losses on securities, fair value, total	767,400	1,690,486
Gross unrealized losses on securities, unrealized losses, total	(56,403)	(95,912)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	37,207	64,288
Gross unrealized losses on securities, less than 12 months, unrealized losses	(813)	(1,639)
Gross unrealized losses on securities, 12 months or more, fair value	12,226	13,806
Gross unrealized losses on securities, 12 months or more, unrealized losses	(891)	(985)
Gross unrealized losses on securities, fair value, total	49,433	78,094
Gross unrealized losses on securities, unrealized losses, total	(1,704)	(2,624)
Equity securities | Common Stock
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	227	623
Gross unrealized losses on securities, less than 12 months, unrealized losses	(3)	(7)
Gross unrealized losses on securities, 12 months or more, fair value	0	0
Gross unrealized losses on securities, 12 months or more, unrealized losses	0	0
Gross unrealized losses on securities, fair value, total	227	623
Gross unrealized losses on securities, unrealized losses, total	(3)	(7)
Equity securities | Non-redeemable preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses on securities, less than 12 months, fair value	36,980	63,665
Gross unrealized losses on securities, less than 12 months, unrealized losses	(810)	(1,632)
Gross unrealized losses on securities, 12 months or more, fair value	12,226	13,806
Gross unrealized losses on securities, 12 months or more, unrealized losses	(891)	(985)
Gross unrealized losses on securities, fair value, total	49,206	77,471
Gross unrealized losses on securities, unrealized losses, total	$ (1,701)	$ (2,617)