Change in Total Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Opening valuation allowance	$ 20,091	$ 21,094	$ 24,654
Reduction during the year	(7,299)	(3,499)	(8,662)
Addition during the year	1,954	2,496	5,102
Closing valuation allowance	$ 14,746	$ 20,091	$ 21,094