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Derivative instruments and hedging activities - Narrative (Details)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
country
Mar. 31, 2017
Dec. 31, 2017
USD ($)
Derivative [Line Items]      
Number of countries for which entity has operations (over) | country 50    
Percentage of sales outside of the Americas during the period 62.00% 61.00%  
Period of protection against the reduction in value caused by a fluctuation, minimum (in number of years) 1 year    
Period of protection against the reduction in value caused by a fluctuation, maximum (in number of years) 3 years    
Foreign currency forward contracts notional amount $ 343,933   $ 318,974
Cost of sales      
Derivative [Line Items]      
Gains (losses) expected to be reclassified from AOCI to earnings 1,900    
Forward Contracts | Net Sales      
Derivative [Line Items]      
Gains (losses) expected to be reclassified from AOCI to earnings (9,900)    
Forward Contracts | Operating Expenses      
Derivative [Line Items]      
Gains (losses) expected to be reclassified from AOCI to earnings 1,900    
Other Derivatives      
Derivative [Line Items]      
Foreign currency forward contracts notional amount $ 52,000   $ 60,000
Maximum      
Derivative [Line Items]      
Duration of derivative contracts entered into by the entity to hedge risk of loss 21 months   24 months
Maximum | Forward Contracts      
Derivative [Line Items]      
Percentage of derivative risk hedged 100.00%    
Duration of derivative contracts entered into by the entity to hedge risk of loss 36 months    
Maximum | Other Derivatives      
Derivative [Line Items]      
Percentage of derivative risk hedged 90.00%    
Duration of derivative contracts entered into by the entity to hedge risk of loss 90 days