Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
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	$ 1,754,536	$ 2,437,278
Gross Unrealized Losses - Less than 12 months	59,400	73,639
Estimated Fair Value - 12 months or greater	513,104	1,068,336
Gross Unrealized Losses - 12 months or greater	38,613	59,659
Estimated Fair Value	2,267,640	3,505,614
Gross Unrealized Losses	98,013	133,298
Equity securities
Estimated Fair Values And Gross Unrealized Losses, OTTI Impairment Losses Reported In AOCI [Line Items]
Estimated Fair Value - Less than 12 months	29,482	11,619
Gross Unrealized Losses - Less than 12 months	545	235
Estimated Fair Value - 12 months or greater	6,649	22,645
Gross Unrealized Losses - 12 months or greater	904	1,386
Estimated Fair Value	36,131	34,264
Gross Unrealized Losses	1,449	1,621
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	404,018	469,408
Gross Unrealized Losses - Less than 12 months	30,978	33,311
Estimated Fair Value - 12 months or greater	52,740	51,539
Gross Unrealized Losses - 12 months or greater	10,216	10,805
Estimated Fair Value	456,758	520,947
Gross Unrealized Losses	41,194	44,116
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	1,350,518	1,967,870
Gross Unrealized Losses - Less than 12 months	28,422	40,328
Estimated Fair Value - 12 months or greater	460,364	1,016,797
Gross Unrealized Losses - 12 months or greater	28,397	48,854
Estimated Fair Value	1,810,882	2,984,667
Gross Unrealized Losses	56,819	89,182
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	357,118	415,886
Gross Unrealized Losses - Less than 12 months	28,279	29,316
Estimated Fair Value - 12 months or greater	25,560	32,567
Gross Unrealized Losses - 12 months or greater	2,557	3,404
Estimated Fair Value	382,678	448,453
Gross Unrealized Losses	30,836	32,720
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	805,091	1,225,767
Gross Unrealized Losses - Less than 12 months	18,419	27,784
Estimated Fair Value - 12 months or greater	227,150	614,294
Gross Unrealized Losses - 12 months or greater	15,576	30,040
Estimated Fair Value	1,032,241	1,840,061
Gross Unrealized Losses	33,995	57,824
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		0
Gross Unrealized Losses - Less than 12 months		0
Estimated Fair Value - 12 months or greater		1,235
Gross Unrealized Losses - 12 months or greater		7
Estimated Fair Value		1,235
Gross Unrealized Losses		7
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	10,308	22,836
Gross Unrealized Losses - Less than 12 months	83	293
Estimated Fair Value - 12 months or greater	12,033	6,284
Gross Unrealized Losses - 12 months or greater	414	225
Estimated Fair Value	22,341	29,120
Gross Unrealized Losses	497	518
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	100,937	78,864
Gross Unrealized Losses - Less than 12 months	1,507	846
Estimated Fair Value - 12 months or greater	62,201	135,414
Gross Unrealized Losses - 12 months or greater	3,228	5,247
Estimated Fair Value	163,138	214,278
Gross Unrealized Losses	4,735	6,093
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	14,478	12,448
Gross Unrealized Losses - Less than 12 months	231	274
Estimated Fair Value - 12 months or greater	6,715	7,108
Gross Unrealized Losses - 12 months or greater	1,707	1,791
Estimated Fair Value	21,193	19,556
Gross Unrealized Losses	1,938	2,065
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	285,839	332,785
Gross Unrealized Losses - Less than 12 months	2,774	4,021
Estimated Fair Value - 12 months or greater	99,896	109,411
Gross Unrealized Losses - 12 months or greater	3,381	4,289
Estimated Fair Value	385,735	442,196
Gross Unrealized Losses	6,155	8,310
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	6,739	3,288
Gross Unrealized Losses - Less than 12 months	240	249
Estimated Fair Value - 12 months or greater	5,522	5,580
Gross Unrealized Losses - 12 months or greater	5,410	5,385
Estimated Fair Value	12,261	8,868
Gross Unrealized Losses	5,650	5,634
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	49,304	78,632
Gross Unrealized Losses - Less than 12 months	162	564
Estimated Fair Value - 12 months or greater	20,733	28,375
Gross Unrealized Losses - 12 months or greater	1,590	2,461
Estimated Fair Value	70,037	107,007
Gross Unrealized Losses	1,752	3,025
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		81,317
Gross Unrealized Losses - Less than 12 months		89
Estimated Fair Value - 12 months or greater		32,959
Gross Unrealized Losses - 12 months or greater		426
Estimated Fair Value		114,276
Gross Unrealized Losses		515
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	0	13,780
Gross Unrealized Losses - Less than 12 months	0	17
Estimated Fair Value - 12 months or greater	13,647	18,998
Gross Unrealized Losses - 12 months or greater	3,128	3,438
Estimated Fair Value	13,647	32,778
Gross Unrealized Losses	3,128	3,455
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	15,375	13,986
Gross Unrealized Losses - Less than 12 months	2,145	3,136
Estimated Fair Value - 12 months or greater	2,910	0
Gross Unrealized Losses - 12 months or greater	128	0
Estimated Fair Value	18,285	13,986
Gross Unrealized Losses	2,273	3,136
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	109,347	156,725
Gross Unrealized Losses - Less than 12 months	5,560	7,007
Estimated Fair Value - 12 months or greater	36,737	76,111
Gross Unrealized Losses - 12 months or greater	1,494	2,946
Estimated Fair Value	146,084	232,836
Gross Unrealized Losses	7,054	9,953
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	20,885	11,619
Gross Unrealized Losses - Less than 12 months	501	235
Estimated Fair Value - 12 months or greater	6,649	19,100
Gross Unrealized Losses - 12 months or greater	904	1,292
Estimated Fair Value	27,534	30,719
Gross Unrealized Losses	1,405	1,527
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	8,597	0
Gross Unrealized Losses - Less than 12 months	44	0
Estimated Fair Value - 12 months or greater	0	3,545
Gross Unrealized Losses - 12 months or greater	0	94
Estimated Fair Value	8,597	3,545
Gross Unrealized Losses	$ 44	$ 94

Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $)
In Thousands, unless otherwise specified