Reinsurance (Income Statement and Comprehensive Income (Loss) Reinsurance Results) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Premiums:
Direct	$ 441,955	$ 417,993
Assumed	60	66
Ceded	(434,100)	(412,302)
Net premiums	7,915	5,757
Policy charges and fee income:
Direct	846,723	781,561
Assumed	121,709	116,339
Ceded	(842,536)	(769,898)
Net policy charges and fee income	125,896	128,002
Net investment income:
Direct	79,149	90,401
Assumed	373	360
Ceded	(1,607)	(1,146)
Net investment income	77,915	89,615
Asset administration fees:
Direct	87,033	80,999
Assumed	0	0
Ceded	(83,560)	(76,812)
Net asset administration fees	3,473	4,187
Other income:
Direct	17,253	15,438
Assumed	(90)	551
Ceded	(52)	(12)
Amortization of reinsurance income	2,185	0
Net other income	19,296	15,977
Realized investment gains (losses), net:
Direct	1,474,762	622,126
Assumed	0	0
Ceded	(1,523,804)	(654,705)
Realized investment gains (losses), net	(49,042)	(32,579)
Policyholders’ benefits (including change in reserves):
Direct	654,638	685,495
Assumed	112,802	129,137
Ceded	(718,485)	(743,145)
Net policyholders’ benefits (including change in reserves)	48,955	71,487
Interest credited to policyholders’ account balances:
Direct	124,734	98,917
Assumed	36,517	33,934
Ceded	(120,453)	(88,091)
Net interest credited to policyholders’ account balances	40,798	44,760
Reinsurance expense allowances and general and administrative expenses, net of capitalization and amortization	(433,912)	(362,236)
Unaffiliated activity
Premiums:
Assumed	100	100
Policy charges and fee income:
Ceded	(2,000)	(700)
Other income:
Assumed	(100)	600
Realized investment gains (losses), net:
Ceded	(38,000)	(8,000)
Policyholders’ benefits (including change in reserves):
Assumed	(100)	400
Ceded	$ (2,000)	$ 3,000