Fair value measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Short-term investments available for sale:
Available-for-sale	$ 237,983	$ 271,396
Total Assets	343,551	352,838
Liabilities
Derivatives	(2,872)	(1,483)
Total Liabilities	$ (2,872)	(1,483)
Short-term investments-available-for sale, contractual maturity	60 months
Quoted Prices In Active Markets For Identical Assets (Level 1)
Short-term investments available for sale:
Total Assets	$ 87,397	62,094
Liabilities
Derivatives	0	0
Total Liabilities	0	0
Significant Other Observable Inputs (Level 2)
Short-term investments available for sale:
Total Assets	256,154	290,744
Liabilities
Derivatives	(2,872)	(1,483)
Total Liabilities	(2,872)	(1,483)
Significant Unobservable Inputs (Level 3)
Short-term investments available for sale:
Total Assets	0	0
Liabilities
Derivatives	0	0
Total Liabilities	0	0
Money Market Accounts
Assets
Cash and cash equivalents available for sale	87,397	62,094
Money Market Accounts \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Assets
Cash and cash equivalents available for sale	87,397	62,094
Money Market Accounts \| Significant Other Observable Inputs (Level 2)
Assets
Cash and cash equivalents available for sale	0	0
Money Market Accounts \| Significant Unobservable Inputs (Level 3)
Assets
Cash and cash equivalents available for sale	0	0
Corporate Notes and Bonds
Assets
Cash and cash equivalents available for sale	9,962	9,979
Corporate Notes and Bonds \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Assets
Cash and cash equivalents available for sale	0	0
Corporate Notes and Bonds \| Significant Other Observable Inputs (Level 2)
Assets
Cash and cash equivalents available for sale	9,962	9,979
Corporate Notes and Bonds \| Significant Unobservable Inputs (Level 3)
Assets
Cash and cash equivalents available for sale	0	0
Corporate bonds
Short-term investments available for sale:
Available-for-sale	237,983	234,473
Liabilities
Cash equivalents denominated in Euros	5,000
Corporate bonds \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Short-term investments available for sale:
Available-for-sale	0	0
Corporate bonds \| Significant Other Observable Inputs (Level 2)
Short-term investments available for sale:
Available-for-sale	237,983	234,473
Corporate bonds \| Significant Unobservable Inputs (Level 3)
Short-term investments available for sale:
Available-for-sale	0	0
U.S. Treasuries and agencies
Short-term investments available for sale:
Available-for-sale		36,923
U.S. treasuries and agencies		36,923
U.S. Treasuries and agencies \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Short-term investments available for sale:
U.S. treasuries and agencies		0
U.S. Treasuries and agencies \| Significant Other Observable Inputs (Level 2)
Short-term investments available for sale:
U.S. treasuries and agencies		36,923
U.S. Treasuries and agencies \| Significant Unobservable Inputs (Level 3)
Short-term investments available for sale:
U.S. treasuries and agencies		0
Derivative
Short-term investments available for sale:
Derivatives	8,209	9,369
Derivative \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Short-term investments available for sale:
Derivatives	0	0
Derivative \| Significant Other Observable Inputs (Level 2)
Short-term investments available for sale:
Derivatives	8,209	9,369
Derivative \| Significant Unobservable Inputs (Level 3)
Short-term investments available for sale:
Derivatives	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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