Investments (Fair Value and Losses by Investment Category and Legth of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 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	$ 2,467,452	$ 5,407,190
Gross Unrealized Losses - Less than 12 months	31,209	234,184
Estimated Fair Value - 12 months or greater	1,777,675	554,529
Gross Unrealized Losses - 12 months or greater	78,536	80,715
Estimated Fair Value	4,245,127	5,961,719
Gross Unrealized Losses	109,745	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	6,705	270,220
Gross Unrealized Losses - Less than 12 months	487	7,227
Estimated Fair Value - 12 months or greater	47,365	32,551
Gross Unrealized Losses - 12 months or greater	2,070	2,474
Estimated Fair Value	54,070	302,771
Gross Unrealized Losses	2,557	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	195,558	399,584
Gross Unrealized Losses - Less than 12 months	2,502	11,062
Estimated Fair Value - 12 months or greater	39,935	85,573
Gross Unrealized Losses - 12 months or greater	8,777	17,580
Estimated Fair Value	235,493	485,157
Gross Unrealized Losses	11,279	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	2,271,894	5,007,606
Gross Unrealized Losses - Less than 12 months	28,707	223,122
Estimated Fair Value - 12 months or greater	1,737,740	468,956
Gross Unrealized Losses - 12 months or greater	69,759	63,135
Estimated Fair Value	4,009,634	5,476,562
Gross Unrealized Losses	98,466	286,257
Corporate 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	165,552	283,603
Gross Unrealized Losses - Less than 12 months	2,181	9,451
Estimated Fair Value - 12 months or greater	19,206	38,256
Gross Unrealized Losses - 12 months or greater	1,359	3,892
Estimated Fair Value	184,758	321,859
Gross Unrealized Losses	3,540	13,343
Corporate 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	1,624,031	3,141,179
Gross Unrealized Losses - Less than 12 months	21,638	148,895
Estimated Fair Value - 12 months or greater	1,062,513	301,303
Gross Unrealized Losses - 12 months or greater	36,925	40,548
Estimated Fair Value	2,686,544	3,442,482
Gross Unrealized Losses	58,563	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	20,728	188,491
Gross Unrealized Losses - Less than 12 months	413	14,419
Estimated Fair Value - 12 months or greater	74,864	12,029
Gross Unrealized Losses - 12 months or greater	3,532	2,429
Estimated Fair Value	95,592	200,520
Gross Unrealized Losses	3,945	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	16,411	62,146
Gross Unrealized Losses - Less than 12 months	137	1,075
Estimated Fair Value - 12 months or greater	3,576	3,945
Gross Unrealized Losses - 12 months or greater	129	254
Estimated Fair Value	19,987	66,091
Gross Unrealized Losses	266	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	74,009	283,967
Gross Unrealized Losses - Less than 12 months	2,365	15,900
Estimated Fair Value - 12 months or greater	122,444	23,068
Gross Unrealized Losses - 12 months or greater	7,337	1,688
Estimated Fair Value	196,453	307,035
Gross Unrealized Losses	9,702	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	11,334	28,670
Gross Unrealized Losses - Less than 12 months	183	415
Estimated Fair Value - 12 months or greater	10,747	32,392
Gross Unrealized Losses - 12 months or greater	2,652	5,498
Estimated Fair Value	22,081	61,062
Gross Unrealized Losses	2,835	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	133,606	255,656
Gross Unrealized Losses - Less than 12 months	1,137	4,916
Estimated Fair Value - 12 months or greater	130,015	56,668
Gross Unrealized Losses - 12 months or greater	5,083	4,983
Estimated Fair Value	263,621	312,324
Gross Unrealized Losses	6,220	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	6,406	10,980
Gross Unrealized Losses - 12 months or greater	4,637	7,936
Estimated Fair Value	6,406	26,742
Gross Unrealized Losses	4,637	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	28,099	219,110
Gross Unrealized Losses - Less than 12 months	206	3,725
Estimated Fair Value - 12 months or greater	39,222	20,068
Gross Unrealized Losses - 12 months or greater	4,191	5,745
Estimated Fair Value	67,321	239,178
Gross Unrealized Losses	4,397	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	10,819	133,697
Gross Unrealized Losses - Less than 12 months	9	4,469
Estimated Fair Value - 12 months or greater	75,730	4,406
Gross Unrealized Losses - 12 months or greater	1,687	279
Estimated Fair Value	86,549	138,103
Gross Unrealized Losses	1,696	4,748
State and political subdivisions | 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	13,426	120,193
Gross Unrealized Losses - Less than 12 months	600	9,723
Estimated Fair Value - 12 months or greater	45,879	15,202
Gross Unrealized Losses - 12 months or greater	3,981	4,616
Estimated Fair Value	59,305	135,395
Gross Unrealized Losses	4,581	14,339
Other foreign government, supranational and foreign government-sponsored enterprises | 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	2,261	9,403
Gross Unrealized Losses - Less than 12 months	1	40
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	2,261	9,403
Gross Unrealized Losses	1	40
Other foreign government, supranational and foreign government-sponsored enterprises | 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	367,176	665,313
Gross Unrealized Losses - Less than 12 months	2,339	21,075
Estimated Fair Value - 12 months or greater	187,073	36,212
Gross Unrealized Losses - 12 months or greater	7,023	2,847
Estimated Fair Value	554,249	701,525
Gross Unrealized Losses	9,362	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	6,705	51,386
Gross Unrealized Losses - Less than 12 months	487	5,479
Estimated Fair Value - 12 months or greater	14,902	1
Gross Unrealized Losses - 12 months or greater	1,080	2
Estimated Fair Value	21,607	51,387
Gross Unrealized Losses	1,567	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	0	218,834
Gross Unrealized Losses - Less than 12 months	0	1,748
Estimated Fair Value - 12 months or greater	32,463	32,550
Gross Unrealized Losses - 12 months or greater	990	2,472
Estimated Fair Value	32,463	251,384
Gross Unrealized Losses	$ 990	$ 4,220