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, 2016	Dec. 31, 2015
Changes in Level 3 Financial Liabilities Related to Contingent Consideration [Roll Forward]
Beginning balance	$ 20,829	$ 33,433
Payment	(7,282)	(8,054)
Revaluations	(6,445)	(4,550)
Ending balance	$ 7,102	$ 20,829

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant