Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Beginning valuation allowance	$ 109,274	$ 95,999
Increase as reflected in income tax expense	11,466	17,951
Cumulative translation adjustment	10,649	(4,676)
Ending valuation allowance	$ 131,389	$ 109,274