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	$ 978,823	$ 452,752	$ 665,207
Capitalization	1,551	1,805	873
Amortization - Impact of assumption and experience unlocking and true-ups	145,141	101,424	21,125
Amortization - All other	(94,014)	(81,603)	(206,263)
Change in unrealized investment gains and losses	(10,715)	4,915	11,063
Ceded DSI upon Reinsurance Treaty with Prudential Insurance			(39,253)
Assumed DSI upon Reinsurance Treaty with Pruco Life Insurance Company		499,530
Ending balance	$ 1,020,786	$ 978,823	$ 452,752