Goodwill and Intangible Assets - Schedule of Changes in Intangible Assets, Net of Accumulated Amortization (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Net balance at January 1	$ 77,015	$ 90,068
Additions	110,680	4,420
Amortization expense	(9,434)	(7,885)
Currency translation	4,827	(9,588)
Net balance at December 31	123,000	$ 77,015
Intangible Assets, Net (Including Goodwill)	$ 183,088