SOI Unrealized losses fixed maturities AFS (Details) $ in Thousands	Dec. 31, 2016 USD ($) position	Dec. 31, 2015 USD ($) position
Total fixed maturity investments
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	$ 7,428,519	$ 6,725,965
Less than twelve months, Unrealized loss and OTTI	235,788	230,467
Twelve months or longer, Estimated fair value	1,151,873	821,922
Unrealized loss and OTTI, 12 months or longer	154,441	128,887
Total Estimated fair value	8,580,392	7,547,887
Total Unrealized losses and OTTI	$ 390,229	$ 359,354
Additional disclosure
Total number of securities in an unrealized loss position, Less than twelve months | position	610	558
Total number of securities in an unrealized loss position, twelve months or longer | position	128	106
Total number of securities in an unrealized loss position | position	738	664
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	$ 2,006,588	$ 1,357,822
Less than twelve months, Unrealized loss and OTTI	34,752	4,101
Twelve months or longer, Estimated fair value	10,526	23,604
Unrealized loss and OTTI, 12 months or longer	206	507
Total Estimated fair value	2,017,114	1,381,426
Total Unrealized losses and OTTI	34,958	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	216,154	267,581
Less than twelve months, Unrealized loss and OTTI	5,922	7,903
Twelve months or longer, Estimated fair value	10,498	0
Unrealized loss and OTTI, 12 months or longer	395	0
Total Estimated fair value	226,652	267,581
Total Unrealized losses and OTTI	6,317	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		2,286
Less than twelve months, Unrealized loss and OTTI		5
Twelve months or longer, Estimated fair value		0
Unrealized loss and OTTI, 12 months or longer		0
Total Estimated fair value		2,286
Total Unrealized losses and OTTI		5
Corporate debt securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	4,119,630	4,412,965
Less than twelve months, Unrealized loss and OTTI	170,453	202,874
Twelve months or longer, Estimated fair value	860,153	552,791
Unrealized loss and OTTI, 12 months or longer	138,711	117,507
Total Estimated fair value	4,979,783	4,965,756
Total Unrealized losses and OTTI	309,164	320,381
Asset-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	316,065	247,082
Less than twelve months, Unrealized loss and OTTI	6,971	4,372
Twelve months or longer, Estimated fair value	230,331	182,404
Unrealized loss and OTTI, 12 months or longer	11,417	8,990
Total Estimated fair value	546,396	429,486
Total Unrealized losses and OTTI	18,388	13,362
Residential mortgage-backed securities
Unrealized losses on fixed maturity and equity investments classified as available-for-sale
Less than twelve months, Estimated fair value	16,962	0
Less than twelve months, Unrealized loss and OTTI	102	0
Twelve months or longer, Estimated fair value	14,297	18,625
Unrealized loss and OTTI, 12 months or longer	1,065	1,508
Total Estimated fair value	31,259	18,625
Total Unrealized losses and OTTI	1,167	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	592,508	429,175
Less than twelve months, Unrealized loss and OTTI	17,535	11,154
Twelve months or longer, Estimated fair value	26,068	44,498
Unrealized loss and OTTI, 12 months or longer	2,647	375
Total Estimated fair value	618,576	473,673
Total Unrealized losses and OTTI	20,182	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	160,612	9,054
Less than twelve months, Unrealized loss and OTTI	53	58
Twelve months or longer, Estimated fair value	0	0
Unrealized loss and OTTI, 12 months or longer	0	0
Total Estimated fair value	160,612	9,054
Total Unrealized losses and OTTI	$ 53	$ 58