Fair value measurements - Schedule of Assets And Liabilities Measured On Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Short-term investments available for sale:
Short-term investments available for sale	$ 92,853	$ 237,983
Derivatives	5,363	8,209
Total Assets	180,946	343,551
Derivatives	(10,777)	(2,872)
Total Liabilities	(10,777)	(2,872)
Short-term investments	$ 92,853	237,983
Available-for-sale contractual maturity (in months)	60 months
Europe
Short-term investments available for sale:
Short-term investments	$ 5,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments available for sale:
Derivatives	0	0
Total Assets	82,730	87,397
Derivatives	0	0
Total Liabilities	0	0
Significant Other Observable Inputs (Level 2)
Short-term investments available for sale:
Derivatives	5,363	8,209
Total Assets	98,216	256,154
Derivatives	(10,777)	(2,872)
Total Liabilities	(10,777)	(2,872)
Significant Unobservable Inputs (Level 3)
Short-term investments available for sale:
Derivatives	0	0
Total Assets	0	0
Derivatives	0	0
Total Liabilities	0	0
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale	82,730	87,397
Money Market Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale	82,730	87,397
Money Market Funds | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale	0	0
Money Market Funds | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale	0	0
Corporate bonds
Short-term investments available for sale:
Short-term investments available for sale	92,853	237,983
Corporate bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Short-term investments available for sale:
Short-term investments available for sale	0	0
Corporate bonds | Significant Other Observable Inputs (Level 2)
Short-term investments available for sale:
Short-term investments available for sale	92,853	237,983
Corporate bonds | Significant Unobservable Inputs (Level 3)
Short-term investments available for sale:
Short-term investments available for sale	$ 0	0
U.S. treasuries and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale		9,962
U.S. treasuries and agencies | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale		0
U.S. treasuries and agencies | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale		9,962
U.S. treasuries and agencies | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents available for sale		$ 0