Changes in Variable Annuity Guaranteed Minimum Death Benefits, Guaranteed Minimum Income Benefits and Guaranteed Minimum Withdrawal Benefits Liabilities (Detail) - Variable Annuity Contracts - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
GMDB
Liabilities For Guarantees On Long Duration Contracts [Line Items]
Guaranteed benefits incurred	$ 5,969	$ 6,380
Guaranteed benefits paid	(4,634)	(6,114)
Unlocking	(13,657)	7,471
Total	(12,322)	7,737
GMIB
Liabilities For Guarantees On Long Duration Contracts [Line Items]
Guaranteed benefits incurred	3,061	3,236
Guaranteed benefits paid	(1,294)	(98)
Unlocking	(13,105)	7,091
Total	(11,338)	10,229
GMWB
Liabilities For Guarantees On Long Duration Contracts [Line Items]
Change in fair value reserves	(6,748)	13,446
Total	$ (6,748)	$ 13,446