Summary of Investments (Details 6) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014 position	Dec. 31, 2013 position
Fixed maturities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	$ 1,536,210	$ 5,763,951
Less than twelve months, Unrealized loss and OTTI	18,372	207,170
Twelve months or longer, Estimated fair value	1,376,083	885,337
Twelve months or longer, Unrealized loss and OTTI	92,304	101,052
Total Estimated fair value	2,912,293	6,649,288
Total Unrealized losses and OTTI	110,676	308,222
Additional disclosure
Total number of securities in an unrealized loss position, Less than twelve months	154	458
Total number of securities in an unrealized loss position, twelve months or longer	177	109
Total number of securities in an unrealized loss position	331	567
Increase (decrease) in total unrealized losses and other-than-temporary impairment losses	(197,546)
Decrease in total unrealized losses and other-than-temporary impairment losses (as a percent)	64.00%
Increase (decrease) in less than twelve months unrealized losses and other-than-temporary impairment losses	(188,798)
Increase (decrease) in greater than twelve months unrealized losses and other-than-temporary impairment losses	(8,748)
U.S. government direct obligations and U.S. agencies
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	37,264	2,399,373
Less than twelve months, Unrealized loss and OTTI	115	23,156
Twelve months or longer, Estimated fair value	126,905	5,192
Twelve months or longer, Unrealized loss and OTTI	3,194	217
Total Estimated fair value	164,169	2,404,565
Total Unrealized losses and OTTI	3,309	23,373
Obligations of U.S. states and their subdivisions
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	53,528	214,979
Less than twelve months, Unrealized loss and OTTI	600	16,713
Twelve months or longer, Estimated fair value	53,547	837
Twelve months or longer, Unrealized loss and OTTI	2,146	239
Total Estimated fair value	107,075	215,816
Total Unrealized losses and OTTI	2,746	16,952
Foreign government securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	2,493	2,603
Less than twelve months, Unrealized loss and OTTI	2	14
Twelve months or longer, Estimated fair value	0	0
Twelve months or longer, Unrealized loss and OTTI	0	0
Total Estimated fair value	2,493	2,603
Total Unrealized losses and OTTI	2	14
Corporate debt securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	1,168,237	2,632,093
Less than twelve months, Unrealized loss and OTTI	14,295	144,367
Twelve months or longer, Estimated fair value	852,422	511,376
Twelve months or longer, Unrealized loss and OTTI	68,659	79,165
Total Estimated fair value	2,020,659	3,143,469
Total Unrealized losses and OTTI	82,954	223,532
Additional disclosure
Unrealized losses and OTTI over twelve months on securities (as a percent)	74.00%
Corporate debt securities | Non-investment grade
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Twelve months or longer, Unrealized loss and OTTI	9,202
Perpetual debt investments
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Twelve months or longer, Unrealized loss and OTTI	8,146
Asset-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	150,583	305,377
Less than twelve months, Unrealized loss and OTTI	2,352	12,763
Twelve months or longer, Estimated fair value	220,335	305,740
Twelve months or longer, Unrealized loss and OTTI	12,113	16,387
Total Estimated fair value	370,918	611,117
Total Unrealized losses and OTTI	14,465	29,150
Additional disclosure
Unrealized losses and OTTI over twelve months on securities (as a percent)	13.00%
Residential mortgage-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	5,333	32,131
Less than twelve months, Unrealized loss and OTTI	11	3,454
Twelve months or longer, Estimated fair value	24,667	1,011
Twelve months or longer, Unrealized loss and OTTI	2,785	19
Total Estimated fair value	30,000	33,142
Total Unrealized losses and OTTI	2,796	3,473
Commercial mortgage-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	108,115	177,395
Less than twelve months, Unrealized loss and OTTI	729	6,703
Twelve months or longer, Estimated fair value	98,207	48,825
Twelve months or longer, Unrealized loss and OTTI	3,407	4,812
Total Estimated fair value	206,322	226,220
Total Unrealized losses and OTTI	4,136	11,515
Collateralized debt obligations
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	10,657	0
Less than twelve months, Unrealized loss and OTTI	268	0
Twelve months or longer, Estimated fair value	0	12,356
Twelve months or longer, Unrealized loss and OTTI	0	213
Total Estimated fair value	10,657	12,356
Total Unrealized losses and OTTI	$ 268	$ 213