Deferred Policy Acquisition Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Balance, beginning of year	$ 1,341,093	$ 5,129,931	$ 5,081,938
Capitalization of commissions, sales and issue expenses	278,892	316,828	616,002
Amortization-Impact of assumption and experience unlocking and true-ups	(16,140)	130,652	112,039
Amortization-All other	(78,867)	(758,753)	(771,208)
Change in unrealized investment gains and losses	(5,363)	(28,723)	91,160
Other	(143,404)	(3,448,842)	0
Balance, end of year	$ 1,376,211	$ 1,341,093	$ 5,129,931