Derivative instruments (Schedule of Derivative Instruments, Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative instruments	$ 41,259	$ 11,833
Derivative fair value of non-current asset	54,735	35,069
Derivative fair value of non-current liability	3,192	7,506
Derivatives Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Derivative instruments	(45)	0
Derivatives Not Designated as Hedging Instrument \| Forward Contracts \| Other Receivables
Derivatives, Fair Value [Line Items]
Derivative instruments	99	0
Derivatives Not Designated as Hedging Instrument \| Forward Contracts \| Accrued Payroll and Other Liabilities
Derivatives, Fair Value [Line Items]
Derivative instruments	(144)	0
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments
Derivatives, Fair Value [Line Items]
Derivative instruments	41,304	11,833
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments \| Derivative Instruments
Derivatives, Fair Value [Line Items]
Derivative fair value of non-current asset	54,735	35,069
Derivative fair value of current liability	10,687	15,522
Derivative fair value of non-current liability	3,192	7,506
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments \| Forward Contracts \| Other Receivables
Derivatives, Fair Value [Line Items]
Derivative instruments	628	309
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments \| Forward Contracts \| Accrued Payroll and Other Liabilities
Derivatives, Fair Value [Line Items]
Derivative instruments	(180)	(517)
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments \| Cross-Currency Interest Rate Swaps \| Derivative Instruments
Derivatives, Fair Value [Line Items]
Derivative instruments	29,141	7,835
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments \| Call Spread \| Derivative Instruments
Derivatives, Fair Value [Line Items]
Derivative instruments	16,867	15,114
Cash Flow Hedging \| Derivatives Designated As Hedging Instruments \| Coupon-only Swap \| Derivative Instruments
Derivatives, Fair Value [Line Items]
Derivative instruments	$ (5,152)	$ (10,908)

Derivative Fair Value Of Current Liability

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- Definition

Fair value, after the effects of master netting arrangements, of a 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, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ 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 (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

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- Definition

Fair value of the assets less the liabilities of a derivative or group of derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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Fair value, after the effects of master netting arrangements, of a 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, expected to be settled after one year or the normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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+ References

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