Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	$ 2,567,914	$ 5,407,190
Gross Unrealized Losses - Less than 12 months	38,133	234,184
Estimated Fair Value - 12 months or greater	1,450,686	554,529
Gross Unrealized Losses - 12 months or greater	79,791	80,715
Estimated Fair Value	4,018,600	5,961,719
Gross Unrealized Losses	117,924	314,899
Equity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	28,317	270,220
Gross Unrealized Losses - Less than 12 months	377	7,227
Estimated Fair Value - 12 months or greater	45,710	32,551
Gross Unrealized Losses - 12 months or greater	2,551	2,474
Estimated Fair Value	74,027	302,771
Gross Unrealized Losses	2,928	9,701
Non-investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	473,448	399,584
Gross Unrealized Losses - Less than 12 months	9,932	11,062
Estimated Fair Value - 12 months or greater	51,014	85,573
Gross Unrealized Losses - 12 months or greater	9,205	17,580
Estimated Fair Value	524,462	485,157
Gross Unrealized Losses	19,137	28,642
Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	2,094,466	5,007,606
Gross Unrealized Losses - Less than 12 months	28,201	223,122
Estimated Fair Value - 12 months or greater	1,399,672	468,956
Gross Unrealized Losses - 12 months or greater	70,586	63,135
Estimated Fair Value	3,494,138	5,476,562
Gross Unrealized Losses	98,787	286,257
Corporate Debt Securities [Member] | Non-investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	428,285	283,603
Gross Unrealized Losses - Less than 12 months	8,710	9,451
Estimated Fair Value - 12 months or greater	31,577	38,256
Gross Unrealized Losses - 12 months or greater	2,344	3,892
Estimated Fair Value	459,862	321,859
Gross Unrealized Losses	11,054	13,343
Corporate Debt Securities [Member] | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	1,381,925	3,141,179
Gross Unrealized Losses - Less than 12 months	20,285	148,895
Estimated Fair Value - 12 months or greater	787,728	301,303
Gross Unrealized Losses - 12 months or greater	41,002	40,548
Estimated Fair Value	2,169,653	3,442,482
Gross Unrealized Losses	61,287	189,443
Canadian and Canadian provincial governments | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	53,864	188,491
Gross Unrealized Losses - Less than 12 months	427	14,419
Estimated Fair Value - 12 months or greater	27,870	12,029
Gross Unrealized Losses - 12 months or greater	1,224	2,429
Estimated Fair Value	81,734	200,520
Gross Unrealized Losses	1,651	16,848
Residential mortgage-backed securities | Non-investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	19,548	62,146
Gross Unrealized Losses - Less than 12 months	206	1,075
Estimated Fair Value - 12 months or greater	3,477	3,945
Gross Unrealized Losses - 12 months or greater	155	254
Estimated Fair Value	23,025	66,091
Gross Unrealized Losses	361	1,329
Residential mortgage-backed securities | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	91,041	283,967
Gross Unrealized Losses - Less than 12 months	1,139	15,900
Estimated Fair Value - 12 months or greater	148,006	23,068
Gross Unrealized Losses - 12 months or greater	8,672	1,688
Estimated Fair Value	239,047	307,035
Gross Unrealized Losses	9,811	17,588
Asset-backed securities | Non-investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	9,642	28,670
Gross Unrealized Losses - Less than 12 months	161	415
Estimated Fair Value - 12 months or greater	9,514	32,392
Gross Unrealized Losses - 12 months or greater	2,143	5,498
Estimated Fair Value	19,156	61,062
Gross Unrealized Losses	2,304	5,913
Asset-backed securities | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	234,958	255,656
Gross Unrealized Losses - Less than 12 months	2,074	4,916
Estimated Fair Value - 12 months or greater	121,589	56,668
Gross Unrealized Losses - 12 months or greater	4,656	4,983
Estimated Fair Value	356,547	312,324
Gross Unrealized Losses	6,730	9,899
Commercial mortgage-backed securities | Non-investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	0	15,762
Gross Unrealized Losses - Less than 12 months	0	81
Estimated Fair Value - 12 months or greater	6,446	10,980
Gross Unrealized Losses - 12 months or greater	4,563	7,936
Estimated Fair Value	6,446	26,742
Gross Unrealized Losses	4,563	8,017
Commercial mortgage-backed securities | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	103,327	219,110
Gross Unrealized Losses - Less than 12 months	922	3,725
Estimated Fair Value - 12 months or greater	40,865	20,068
Gross Unrealized Losses - 12 months or greater	2,950	5,745
Estimated Fair Value	144,192	239,178
Gross Unrealized Losses	3,872	9,470
US Government Agencies Debt Securities [Member] | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	40,941	133,697
Gross Unrealized Losses - Less than 12 months	70	4,469
Estimated Fair Value - 12 months or greater	71,551	4,406
Gross Unrealized Losses - 12 months or greater	1,682	279
Estimated Fair Value	112,492	138,103
Gross Unrealized Losses	1,752	4,748
US States and Political Subdivisions Debt Securities [Member] | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	40,692	120,193
Gross Unrealized Losses - Less than 12 months	124	9,723
Estimated Fair Value - 12 months or greater	45,205	15,202
Gross Unrealized Losses - 12 months or greater	4,654	4,616
Estimated Fair Value	85,897	135,395
Gross Unrealized Losses	4,778	14,339
Foreign Government Debt Securities [Member] | Non-investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	15,973	9,403
Gross Unrealized Losses - Less than 12 months	855	40
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	15,973	9,403
Gross Unrealized Losses	855	40
Foreign Government Debt Securities [Member] | Investment grade securities | Fixed maturity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	147,718	665,313
Gross Unrealized Losses - Less than 12 months	3,160	21,075
Estimated Fair Value - 12 months or greater	156,858	36,212
Gross Unrealized Losses - 12 months or greater	5,746	2,847
Estimated Fair Value	304,576	701,525
Gross Unrealized Losses	8,906	23,922
Nonredeemable Preferred Stock [Member] | Equity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	3,765	51,386
Gross Unrealized Losses - Less than 12 months	287	5,479
Estimated Fair Value - 12 months or greater	17,149	1
Gross Unrealized Losses - 12 months or greater	1,411	2
Estimated Fair Value	20,914	51,387
Gross Unrealized Losses	1,698	5,481
Other equity securities | Equity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	24,552	218,834
Gross Unrealized Losses - Less than 12 months	90	1,748
Estimated Fair Value - 12 months or greater	28,561	32,550
Gross Unrealized Losses - 12 months or greater	1,140	2,472
Estimated Fair Value	53,113	251,384
Gross Unrealized Losses	$ 1,230	$ 4,220