Income Taxes (Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets:
Policy benefit reserves	$ 1,842,049	$ 2,354,786
Other than temporary impairments	11,262	15,681
Amounts due reinsurer	6,852	1,321
Other policyholder funds	3,724	6,474
Deferred compensation	3,827	7,963
Share-based compensation	3,383	5,407
State net operating loss carryforwards	3,196	3,745
Other	10,253	11,367
Gross deferred tax assets	1,884,546	2,406,744
Deferred income tax liabilities:
Deferred policy acquisition costs and deferred sales inducements	(1,212,509)	(1,951,333)
Net unrealized gains on available for sale fixed maturity and equity securities	(220,533)	(170,925)
Derivative instruments	(179,776)	(75,405)
Policy benefit reserves	(197,233)	0
Investment income items	(34,849)	(39,118)
Other	(1,499)	(1,385)
Gross deferred tax liabilities	(1,846,399)	(2,238,166)
Net deferred income tax asset	$ 38,147	$ 168,578