Investments (Fair Value and Losses by Investment Category and Legth of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 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	$ 3,585,265	$ 5,407,190
Gross Unrealized Losses - Less than 12 months	108,055	234,184
Estimated Fair Value - 12 months or greater	602,972	554,529
Gross Unrealized Losses - 12 months or greater	66,929	80,715
Estimated Fair Value	4,188,237	5,961,719
Gross Unrealized Losses	174,984	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	20,765	270,220
Gross Unrealized Losses - Less than 12 months	2,660	7,227
Estimated Fair Value - 12 months or greater	32,834	32,551
Gross Unrealized Losses - 12 months or greater	1,663	2,474
Estimated Fair Value	53,599	302,771
Gross Unrealized Losses	4,323	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	221,456	399,584
Gross Unrealized Losses - Less than 12 months	4,127	11,062
Estimated Fair Value - 12 months or greater	59,406	85,573
Gross Unrealized Losses - 12 months or greater	9,514	17,580
Estimated Fair Value	280,862	485,157
Gross Unrealized Losses	13,641	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	3,363,809	5,007,606
Gross Unrealized Losses - Less than 12 months	103,928	223,122
Estimated Fair Value - 12 months or greater	543,566	468,956
Gross Unrealized Losses - 12 months or greater	57,415	63,135
Estimated Fair Value	3,907,375	5,476,562
Gross Unrealized Losses	161,343	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	191,113	283,603
Gross Unrealized Losses - Less than 12 months	3,886	9,451
Estimated Fair Value - 12 months or greater	43,178	38,256
Gross Unrealized Losses - 12 months or greater	2,721	3,892
Estimated Fair Value	234,291	321,859
Gross Unrealized Losses	6,607	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	2,057,301	3,141,179
Gross Unrealized Losses - Less than 12 months	64,535	148,895
Estimated Fair Value - 12 months or greater	311,738	301,303
Gross Unrealized Losses - 12 months or greater	31,273	40,548
Estimated Fair Value	2,369,039	3,442,482
Gross Unrealized Losses	95,808	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	114,845	188,491
Gross Unrealized Losses - Less than 12 months	6,334	14,419
Estimated Fair Value - 12 months or greater	12,421	12,029
Gross Unrealized Losses - 12 months or greater	1,603	2,429
Estimated Fair Value	127,266	200,520
Gross Unrealized Losses	7,937	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	26,209	62,146
Gross Unrealized Losses - Less than 12 months	197	1,075
Estimated Fair Value - 12 months or greater	1,776	3,945
Gross Unrealized Losses - 12 months or greater	50	254
Estimated Fair Value	27,985	66,091
Gross Unrealized Losses	247	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	190,212	283,967
Gross Unrealized Losses - Less than 12 months	9,802	15,900
Estimated Fair Value - 12 months or greater	32,621	23,068
Gross Unrealized Losses - 12 months or greater	3,294	1,688
Estimated Fair Value	222,833	307,035
Gross Unrealized Losses	13,096	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	1,694	28,670
Gross Unrealized Losses - Less than 12 months	10	415
Estimated Fair Value - 12 months or greater	8,483	32,392
Gross Unrealized Losses - 12 months or greater	1,625	5,498
Estimated Fair Value	10,177	61,062
Gross Unrealized Losses	1,635	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	214,774	255,656
Gross Unrealized Losses - Less than 12 months	3,140	4,916
Estimated Fair Value - 12 months or greater	79,532	56,668
Gross Unrealized Losses - 12 months or greater	7,023	4,983
Estimated Fair Value	294,306	312,324
Gross Unrealized Losses	10,163	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	5,969	10,980
Gross Unrealized Losses - 12 months or greater	5,118	7,936
Estimated Fair Value	5,969	26,742
Gross Unrealized Losses	5,118	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	106,146	219,110
Gross Unrealized Losses - Less than 12 months	1,295	3,725
Estimated Fair Value - 12 months or greater	26,181	20,068
Gross Unrealized Losses - 12 months or greater	5,443	5,745
Estimated Fair Value	132,327	239,178
Gross Unrealized Losses	6,738	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	75,193	133,697
Gross Unrealized Losses - Less than 12 months	2,777	4,469
Estimated Fair Value - 12 months or greater	4,104	4,406
Gross Unrealized Losses - 12 months or greater	190	279
Estimated Fair Value	79,297	138,103
Gross Unrealized Losses	2,967	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	103,058	120,193
Gross Unrealized Losses - Less than 12 months	5,440	9,723
Estimated Fair Value - 12 months or greater	8,158	15,202
Gross Unrealized Losses - 12 months or greater	3,760	4,616
Estimated Fair Value	111,216	135,395
Gross Unrealized Losses	9,200	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	2,440	9,403
Gross Unrealized Losses - Less than 12 months	34	40
Estimated Fair Value - 12 months or greater	0	0
Gross Unrealized Losses - 12 months or greater	0	0
Estimated Fair Value	2,440	9,403
Gross Unrealized Losses	34	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	502,280	665,313
Gross Unrealized Losses - Less than 12 months	10,605	21,075
Estimated Fair Value - 12 months or greater	68,811	36,212
Gross Unrealized Losses - 12 months or greater	4,829	2,847
Estimated Fair Value	571,091	701,525
Gross Unrealized Losses	15,434	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	20,765	51,386
Gross Unrealized Losses - Less than 12 months	2,660	5,479
Estimated Fair Value - 12 months or greater	1	1
Gross Unrealized Losses - 12 months or greater	2	2
Estimated Fair Value	20,766	51,387
Gross Unrealized Losses	2,662	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	32,833	32,550
Gross Unrealized Losses - 12 months or greater	1,661	2,472
Estimated Fair Value	32,833	251,384
Gross Unrealized Losses	$ 1,661	$ 4,220