Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill And Intangible Assets Disclosure [Abstract]
Beginning Balance	$ 373,117	$ 320,761	$ 335,402
Business acquisitions		54,631
Foreign currency translation adjustments	12,175	(2,275)	(14,641)
Ending Balance	$ 385,292	$ 373,117	$ 320,761