Certain Long-Duration Contracts with Guarantees (Sales Inducements) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in Deferred Sales Inducements [Roll Forward]
Beginning balance	$ 1,020,786	$ 978,823	$ 452,752
Capitalization	2,888	1,551	1,805
Amortization - Impact of assumption and experience unlocking and true-ups	(5,713)	145,141	101,424
Amortization - All other	(149,236)	(94,014)	(81,603)
Change in unrealized investment gains and losses	20,873	(10,715)	4,915
Assumed DSI upon Reinsurance Treaty with Pruco Life Insurance Company			499,530
Ending balance	$ 889,598	$ 1,020,786	$ 978,823