Fair value measurement - reconciliation of changes in three financial liabilities measured at fair value on recurring (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes in Level 3 Financial Liabilities Related to Contingent Consideration [Roll Forward]
Beginning balance	$ 7,102	$ 20,829
Initial estimate upon acquisition	261,733	0
Payments	(335)	(7,282)
Revaluations	3,575	(6,445)
Translation adjustment	61	0
Ending balance	$ 272,136	$ 7,102