Derivative instruments and hedging activities - Fair Value Of Derivative Instruments On Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets	$ 7,799	$ 7,233
Derivative liability	(3,232)	(12,743)
Derivatives Designated As Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative assets	7,007	7,046
Derivative liability	(3,185)	(11,446)
Derivatives Designated As Hedging Instruments \| Foreign Exchange Contract - Short-Term \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Derivative assets	4,980	4,707
Derivatives Designated As Hedging Instruments \| Foreign Exchange Contract - Short-Term \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	(2,286)	(7,487)
Derivatives Designated As Hedging Instruments \| Foreign Exchange Contracts - Long-Term \| Other long-term assets
Derivatives, Fair Value [Line Items]
Derivative assets	2,027	2,339
Derivatives Designated As Hedging Instruments \| Foreign Exchange Contracts - Long-Term \| Other long-term liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	(899)	(3,959)
Derivatives Not Designated As Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative assets	792	187
Derivative liability	(47)	(1,297)
Derivatives Not Designated As Hedging Instruments \| Foreign Exchange Contract - Short-Term \| Prepaid expenses and other current assets
Derivatives, Fair Value [Line Items]
Derivative assets	792	187
Derivatives Not Designated As Hedging Instruments \| Foreign Exchange Contract - Short-Term \| Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability	$ (47)	$ (1,297)

Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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