Changes in Guaranteed Minimum Death Benefits and Guaranteed Minimum Income Benefits Liabilities (Detail) - Variable Annuity Contracts - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
GMDB
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Guaranteed benefits incurred	$ 6,486	$ 6,602	$ 12,866	$ 13,084
Guaranteed benefits paid	(7,184)	(7,987)	(13,298)	(12,785)
Unlocking	(2,630)	3,785	4,841	(725)
Total	(3,328)	2,400	4,409	(426)
GMIB
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Guaranteed benefits incurred	3,529	2,781	6,765	5,662
Guaranteed benefits paid	(1,308)	(290)	(1,406)	(336)
Unlocking	(1,911)	276	5,180	(3,316)
Total	$ 310	$ 2,767	$ 10,539	$ 2,010