Financial instruments - after tax (gain)/loss reclassified from accumulated other comprehensive income into income (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivatives Fair Value [Line Items]
After Tax Gain (Loss) Recognized in OCI	$ 67	$ (2,491)	$ 0
Foreign Currency Exchange Contracts
Derivatives Fair Value [Line Items]
After Tax Gain (Loss) Recognized in OCI	$ 67	$ (2,491)	$ 0

Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580

Name:	us-gaap_OtherComprehensiveIncomeLossDerivativesQualifyingAsHedgesNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration