Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fixed Maturities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 2,437,278	$ 5,407,190
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	73,639	234,184
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,068,336	554,529
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	59,659	80,715
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,505,614	5,961,719
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	133,298	314,899
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,967,870	5,007,606
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	40,328	223,122
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,016,797	468,956
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	48,854	63,135
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,984,667	5,476,562
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	89,182	286,257
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | Corporate Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,225,767	3,141,179
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	27,784	148,895
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	614,294	301,303
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	30,040	40,548
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,840,061	3,442,482
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	57,824	189,443
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | Canadian Provincial Governments [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	188,491
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0	14,419
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,235	12,029
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	7	2,429
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,235	200,520
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	7	16,848
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | Residential Mortgage Backed Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	78,864	283,967
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	846	15,900
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	135,414	23,068
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	5,247	1,688
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	214,278	307,035
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	6,093	17,588
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | Asset-backed Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	332,785	255,656
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	4,021	4,916
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	109,411	56,668
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	4,289	4,983
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	442,196	312,324
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	8,310	9,899
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | Commercial Mortgage Backed Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	78,632	219,110
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	564	3,725
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	28,375	20,068
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	2,461	5,745
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	107,007	239,178
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	3,025	9,470
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | US Government Agencies Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	81,317	133,697
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	89	4,469
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	32,959	4,406
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	426	279
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	114,276	138,103
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	515	4,748
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | US States and Political Subdivisions Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	13,780	120,193
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	17	9,723
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	18,998	15,202
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	3,438	4,616
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	32,778	135,395
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	3,455	14,339
Fixed Maturities [Member] | External Credit Rating, Investment Grade [Member] | Foreign Government Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	156,725	665,313
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	7,007	21,075
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	76,111	36,212
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	2,946	2,847
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	232,836	701,525
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	9,953	23,922
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	469,408	399,584
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	33,311	11,062
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	51,539	85,573
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	10,805	17,580
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	520,947	485,157
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	44,116	28,642
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member] | Corporate Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	415,886	283,603
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	29,316	9,451
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	32,567	38,256
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	3,404	3,892
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	448,453	321,859
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	32,720	13,343
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member] | Residential Mortgage Backed Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	22,836	62,146
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	293	1,075
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	6,284	3,945
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	225	254
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	29,120	66,091
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	518	1,329
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member] | Asset-backed Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	12,448	28,670
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	274	415
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	7,108	32,392
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	1,791	5,498
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	19,556	61,062
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	2,065	5,913
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member] | Commercial Mortgage Backed Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	3,288	15,762
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	249	81
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,580	10,980
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	5,385	7,936
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	8,868	26,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	5,634	8,017
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member] | US States and Political Subdivisions Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	964
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	43
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	964
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	43
Fixed Maturities [Member] | External Credit Rating, Non Investment Grade [Member] | Foreign Government Debt Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	13,986	9,403
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	3,136	40
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, Aggregate Losses	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	13,986	9,403
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	3,136	40
Equity Securities [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	11,619	270,220
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	235	7,227
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	22,645	32,551
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	1,386	2,474
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	34,264	302,771
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	1,621	9,701
Equity Securities [Member] | Nonredeemable Preferred Stock [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	11,619	51,386
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	235	5,479
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	19,100	1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	1,292	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	30,719	51,387
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	1,527	5,481
Equity Securities [Member] | Equity Securities Other Than Non-redeemable Preferred Stock [Member]
Estimated Fair Values And Gross Unrealized Losses OTTI Impairment Losses Reported In AOCI [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	218,834
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Losses	0	1,748
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	3,545	32,550
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses	94	2,472
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,545	251,384
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ 94	$ 4,220