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, 2018	Dec. 31, 2017
Changes in Level 3 Financial Liabilities Related to Contingent Consideration [Roll Forward]
Beginning balance	$ 272,136	$ 7,102
Initial estimate upon acquisition	54,696	261,733
Payments	(75,335)	(335)
Revaluations	52,977	3,575
Translation adjustment	(226)	61
Ending balance	$ 304,248	$ 272,136