Reinsurance (Income Statement Reinsurance Results) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Premiums:
Direct				$ 1,621,531	$ 1,519,992	$ 1,408,833
Assumed				359	0	0
Ceded				(2,447,832)	(1,442,358)	(1,342,627)
Net premiums				(825,942)	77,634	66,206
Policy charges and fee income:
Direct				2,804,446	2,933,271	2,754,115
Assumed				533,648	434,560	477,921
Ceded				(2,550,899)	(1,211,444)	(1,160,997)
Net policy charges and fee income	$ 58,931	$ 526,562	$ 585,493	787,195	2,156,387	2,071,039
Net investment income:
Direct				378,969	419,357	406,620
Assumed				1,411	1,394	1,362
Ceded				(4,430)	(4,164)	(3,964)
Net investment income				375,950	416,587	404,018
Asset administration fees:
Direct				310,178	362,321	377,127
Assumed				0	0	0
Ceded				(225,735)	0	0
Net asset administration fees				84,443	362,321	377,127
Other income:
Direct				50,475	44,223	49,891
Assumed				(161)	0	0
Ceded				21	0	0
Amortization of reinsurance income				(19,228)	11,292	7,936
Net other income				31,107	55,515	57,827
Realized investment gains (losses), net:
Direct				1,263,088	571,702	(4,375,107)
Assumed				0	0	0
Ceded				(504,639)	(780,240)	4,489,174
Realized investment gains (losses), net				758,449	(208,538)	114,067
Policyholders’ benefits (including change in reserves):
Direct				2,456,262	2,064,906	1,863,078
Assumed				596,196	541,371	792,616
Ceded				(3,312,658)	(2,307,127)	(2,301,997)
Net policyholders’ benefits (including change in reserves)	$ (472,610)	$ 100,730	$ (371,880)	(260,200)	299,150	353,697
Interest credited to policyholders’ account balances:
Direct				413,328	477,667	459,982
Assumed				131,953	124,954	117,725
Ceded				(244,061)	(228,410)	(209,392)
Net interest credited to policyholders’ account balances				301,220	374,211	368,315
Net reinsurance expense allowances, net of capitalization and amortization				(840,010)	(354,372)	(390,531)
Unaffiliated
Premiums:
Assumed				400	0	0
Policy charges and fee income:
Ceded				(4,000)	(4,000)	(4,000)
Other income:
Assumed				(200)	0	0
Realized investment gains (losses), net:
Ceded				(30,000)	2,000	0
Policyholders’ benefits (including change in reserves):
Ceded				$ 5,000	$ (14,000)	$ 3,000