Reinsurance (Income Statement Reinsurance Results) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premiums:
Direct	$ 1,720,896	$ 1,621,531	$ 1,519,992
Assumed	194	359	0
Ceded	(1,666,384)	(2,447,832)	(1,442,358)
Net premiums	54,706	(825,942)	77,634
Policy charges and fee income:
Direct	3,459,134	2,804,446	2,933,271
Assumed	473,573	533,648	434,560
Ceded	(3,678,165)	(2,550,899)	(1,211,444)
Net policy charges and fee income	254,542	787,195	2,156,387
Net investment income:
Direct	356,291	378,969	419,357
Assumed	1,484	1,411	1,394
Ceded	(5,365)	(4,430)	(4,164)
Net investment income	352,410	375,950	416,587
Asset administration fees:
Direct	340,461	310,178	362,321
Assumed	0	0	0
Ceded	(322,868)	(225,735)	0
Net asset administration fees	17,593	84,443	362,321
Other income:
Direct	62,830	50,475	44,223
Assumed	390	(161)	0
Ceded	(77)	21	0
Amortization of reinsurance income	4,606	(19,228)	11,292
Net other income	67,749	31,107	55,515
Realized investment gains (losses), net:
Direct	478,117	1,263,088	571,702
Assumed	0	0	0
Ceded	(558,303)	(504,639)	(780,240)
Realized investment gains (losses), net	(80,186)	758,449	(208,538)
Policyholders’ benefits (including change in reserves):
Direct	2,450,810	2,456,262	2,064,906
Assumed	584,909	596,196	541,371
Ceded	(3,074,099)	(3,312,658)	(2,307,127)
Net policyholders’ benefits (including change in reserves)	(38,380)	(260,200)	299,150
Interest credited to policyholders’ account balances:
Direct	350,262	413,328	477,667
Assumed	135,123	131,953	124,954
Ceded	(316,994)	(244,061)	(228,410)
Net interest credited to policyholders’ account balances	168,391	301,220	374,211
Net reinsurance expense allowances, net of capitalization and amortization	(1,302,020)	(840,010)	(354,372)
Unaffiliated
Premiums:
Assumed	200	400	0
Ceded	0
Policy charges and fee income:
Ceded	(8,000)	(4,000)	(4,000)
Other income:
Assumed	400	(200)	0
Realized investment gains (losses), net:
Ceded	(20,000)	(30,000)	2,000
Policyholders’ benefits (including change in reserves):
Assumed	400
Ceded	$ 4,000	$ 5,000	$ (14,000)