Certain Long-Duration Contracts with Guarantees (Sales Inducements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Deferred Sales Inducements [Roll Forward]
Beginning balance	$ 0	$ 684,844	$ 836,791
Capitalization	0	932	6,462
Amortization-Impact of assumption and experience unlocking and true-ups	0	11,817	21,829
Amortization-All other	0	(144,670)	(183,843)
Change in unrealized investment gains (losses)	0	(2,802)	3,605
Other	0	(550,121)
Ending balance	$ 0	$ 0	$ 684,844