Fair value measurements- Assets and liabilities measured at fair value on recurring basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	$ 393	$ 430
Assets, fair value	29,856	42,824
Fair Value, Inputs, Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	3,804	5,197
Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	4	41
Assets, fair value	26,052	37,627
Fair Value, Inputs, Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	389	389
Money Market Funds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	2,306	199
Money Market Funds | Fair Value, Inputs, Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	2,306	199
U.S. government securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	1,498	4,998
U.S. government securities | Fair Value, Inputs, Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	1,498	4,998
Money market accounts
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	23,809	23,809
Money market accounts | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	23,809	23,809
Sovereign government bonds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value		622
Sovereign government bonds | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value		622
Corporate Bonds
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value		9,439
Corporate Bonds | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value		9,439
Government-sponsored enterprise obligations
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	2,243	3,757
Government-sponsored enterprise obligations | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	2,243	3,757
Mutual Funds Held in Rabbi Trust [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	814	622
Mutual Funds Held in Rabbi Trust [Member] | Fair Value, Inputs, Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Assets, fair value	814	622
Rusnano Payment Derivative
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	389	389
Rusnano Payment Derivative | Fair Value, Inputs, Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	389	389
Foreign currency forward contracts
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	4	41
Foreign currency forward contracts | Fair Value, Inputs, Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Liabilities Fair Value disclosure	$ 4	$ 41