Minimum Guarantees - Amounts Paid and Incurred for GMDB (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Balances, January 1,	$ 7,169	$ 10,280	$ 5,566
Incurred guaranteed benefits	3,513	(2,608)	5,634
Paid guaranteed benefits	(819)	(503)	(920)
Balances, December 31,	9,863	7,169	10,280
GMDB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Balances, January 1,	5,096	5,467	5,566
Incurred guaranteed benefits	(294)	132	821
Paid guaranteed benefits	(819)	(503)	(920)
Balances, December 31,	3,983	5,096	5,467
GLWB
Movement in Liabilities for Guarantees on Long-Duration Contracts, Guaranteed Benefit Liability, Gross [Roll Forward]
Balances, January 1,	2,073	4,813	0
Incurred guaranteed benefits	3,807	(2,740)	4,813
Paid guaranteed benefits	0	0	0
Balances, December 31,	$ 5,880	$ 2,073	$ 4,813