Goodwill and Intangible Assets, Net - Schedule of Changes to Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill Roll Forward
Goodwill, beginning balance	$ 613,335	$ 657,671
Additions	86,730	23,191
Foreign currency translation and other adjustments	30,399	(67,527)
Goodwill, ending balance	$ 730,464	$ 613,335