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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
GMDB
Liabilities For Guarantees On Long Duration Contracts [Line Items]
Guaranteed benefits incurred	$ 5,696	$ 6,486	$ 11,665	$ 12,866
Guaranteed benefits paid	(6,791)	(7,184)	(11,425)	(13,298)
Unlocking	(2,803)	(2,630)	(16,460)	4,841
Total	(3,898)	(3,328)	(16,220)	4,409
GMIB
Liabilities For Guarantees On Long Duration Contracts [Line Items]
Guaranteed benefits incurred	2,742	3,529	5,803	6,765
Guaranteed benefits paid	(724)	(1,308)	(2,018)	(1,406)
Unlocking	(5,346)	(1,911)	(18,451)	5,180
Total	(3,328)	310	(14,666)	10,539
GMWB
Liabilities For Guarantees On Long Duration Contracts [Line Items]
Change in fair value reserves	1,093	10,426	(5,655)	23,872
Total	$ 1,093	$ 10,426	$ (5,655)	$ 23,872