Summary of Investments - SOI Unrealized losses fixed maturities AFS (Details 6) $ in Thousands	6 Months Ended
	Jun. 30, 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	$ 1,194,803	$ 6,725,965
Less than twelve months, Unrealized loss and OTTI	49,751	230,467
Twelve months or longer, Estimated fair value	1,277,214	821,922
Twelve months or longer, Unrealized loss and OTTI	148,163	128,887
Total Estimated fair value	2,472,017	7,547,887
Total Unrealized losses and OTTI	$ 197,914	$ 359,354
Additional disclosure
Total number of securities in an unrealized loss position, Less than twelve months | position	98	558
Total number of securities in an unrealized loss position, twelve months or longer | position	143	106
Total number of securities in an unrealized loss position | position	241	664
Decrease (increase) in total unrealized losses and other-than-temporary impairment losses	$ 161,440
Decrease (increase) in total unrealized losses and other-than-temporary impairment losses (as a percent)	45.00%
Increase (decrease) in greater than twelve months unrealized losses and other-than-temporary impairment losses	$ 19,276
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	1,373	$ 1,357,822
Less than twelve months, Unrealized loss and OTTI	10	4,101
Twelve months or longer, Estimated fair value	11,755	23,604
Twelve months or longer, Unrealized loss and OTTI	110	507
Total Estimated fair value	13,128	1,381,426
Total Unrealized losses and OTTI	120	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	632	267,581
Less than twelve months, Unrealized loss and OTTI	87	7,903
Twelve months or longer, Estimated fair value	10,101	0
Twelve months or longer, Unrealized loss and OTTI	94	0
Total Estimated fair value	10,733	267,581
Total Unrealized losses and OTTI	181	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	2,205	2,286
Less than twelve months, Unrealized loss and OTTI	4	5
Twelve months or longer, Estimated fair value	0	0
Twelve months or longer, Unrealized loss and OTTI	0	0
Total Estimated fair value	2,205	2,286
Total Unrealized losses and OTTI	4	5
Corporate debt securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	918,217	4,412,965
Less than twelve months, Unrealized loss and OTTI	44,939	202,874
Twelve months or longer, Estimated fair value	975,449	552,791
Twelve months or longer, Unrealized loss and OTTI	137,595	117,507
Total Estimated fair value	1,893,666	4,965,756
Total Unrealized losses and OTTI	$ 182,534	320,381
Additional disclosure
Unrealized losses and OTTI over twelve months on securities (as a percent)	93.00%
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	$ 17,788
Perpetual debt investments
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Twelve months or longer, Unrealized loss and OTTI	12,838
Asset-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	199,178	247,082
Less than twelve months, Unrealized loss and OTTI	4,215	4,372
Twelve months or longer, Estimated fair value	213,912	182,404
Twelve months or longer, Unrealized loss and OTTI	8,476	8,990
Total Estimated fair value	413,090	429,486
Total Unrealized losses and OTTI	$ 12,691	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	$ 796	0
Less than twelve months, Unrealized loss and OTTI	2	0
Twelve months or longer, Estimated fair value	17,110	18,625
Twelve months or longer, Unrealized loss and OTTI	588	1,508
Total Estimated fair value	17,906	18,625
Total Unrealized losses and OTTI	590	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	62,458	429,175
Less than twelve months, Unrealized loss and OTTI	440	11,154
Twelve months or longer, Estimated fair value	48,887	44,498
Twelve months or longer, Unrealized loss and OTTI	1,300	375
Total Estimated fair value	111,345	473,673
Total Unrealized losses and OTTI	1,740	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	9,944	9,054
Less than twelve months, Unrealized loss and OTTI	54	58
Twelve months or longer, Estimated fair value	0	0
Twelve months or longer, Unrealized loss and OTTI	0	0
Total Estimated fair value	9,944	9,054
Total Unrealized losses and OTTI	$ 54	$ 58