Summary of Investments - SOI Unrealized losses fixed maturities AFS (Details 6) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) position	Dec. 31, 2015 USD ($) position
Fixed maturities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	$ 2,652,167	$ 6,725,965
Less than twelve months, Unrealized loss and OTTI	83,005	230,467
Twelve months or longer, Estimated fair value	1,285,128	821,922
Twelve months or longer, Unrealized loss and OTTI	164,540	128,887
Total Estimated fair value	3,937,295	7,547,887
Total Unrealized losses and OTTI	$ 247,545	$ 359,354
Additional disclosure
Total number of securities in an unrealized loss position, Less than twelve months | position	246	558
Total number of securities in an unrealized loss position, twelve months or longer | position	155	106
Total number of securities in an unrealized loss position | position	401	664
Decrease (increase) in total unrealized losses and other-than-temporary impairment losses	$ 111,809
Decrease (increase) in total unrealized losses and other-than-temporary impairment losses (as a percent)	31.00%
Increase (decrease) in greater than twelve months unrealized losses and other-than-temporary impairment losses	$ 35,653
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	50,371	$ 1,357,822
Less than twelve months, Unrealized loss and OTTI	439	4,101
Twelve months or longer, Estimated fair value	53,275	23,604
Twelve months or longer, Unrealized loss and OTTI	302	507
Total Estimated fair value	103,646	1,381,426
Total Unrealized losses and OTTI	741	4,608
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	10,796	267,581
Less than twelve months, Unrealized loss and OTTI	143	7,903
Twelve months or longer, Estimated fair value	78,883	0
Twelve months or longer, Unrealized loss and OTTI	1,023	0
Total Estimated fair value	89,679	267,581
Total Unrealized losses and OTTI	1,166	7,903
Foreign government securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	2,248	2,286
Less than twelve months, Unrealized loss and OTTI	3	5
Twelve months or longer, Estimated fair value	0	0
Twelve months or longer, Unrealized loss and OTTI	0	0
Total Estimated fair value	2,248	2,286
Total Unrealized losses and OTTI	3	5
Corporate debt securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	2,052,304	4,412,965
Less than twelve months, Unrealized loss and OTTI	74,189	202,874
Twelve months or longer, Estimated fair value	865,541	552,791
Twelve months or longer, Unrealized loss and OTTI	150,756	117,507
Total Estimated fair value	2,917,845	4,965,756
Total Unrealized losses and OTTI	$ 224,945	320,381
Additional disclosure
Unrealized losses and OTTI over twelve months on securities (as a percent)	92.00%
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	$ 19,440
Perpetual debt investments
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Twelve months or longer, Unrealized loss and OTTI	13,166
Asset-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	388,520	247,082
Less than twelve months, Unrealized loss and OTTI	5,968	4,372
Twelve months or longer, Estimated fair value	207,508	182,404
Twelve months or longer, Unrealized loss and OTTI	9,774	8,990
Total Estimated fair value	596,028	429,486
Total Unrealized losses and OTTI	$ 15,742	13,362
Additional disclosure
Unrealized losses and OTTI over twelve months on securities (as a percent)	6.00%
Residential mortgage-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	$ 4,858	0
Less than twelve months, Unrealized loss and OTTI	9	0
Twelve months or longer, Estimated fair value	18,107	18,625
Twelve months or longer, Unrealized loss and OTTI	871	1,508
Total Estimated fair value	22,965	18,625
Total Unrealized losses and OTTI	880	1,508
Commercial mortgage-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	143,070	429,175
Less than twelve months, Unrealized loss and OTTI	2,254	11,154
Twelve months or longer, Estimated fair value	61,814	44,498
Twelve months or longer, Unrealized loss and OTTI	1,814	375
Total Estimated fair value	204,884	473,673
Total Unrealized losses and OTTI	$ 4,068	11,529
Collateralized debt obligations
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value		9,054
Less than twelve months, Unrealized loss and OTTI		58
Twelve months or longer, Estimated fair value		0
Twelve months or longer, Unrealized loss and OTTI		0
Total Estimated fair value		9,054
Total Unrealized losses and OTTI		$ 58