Quarterly report pursuant to Section 13 or 15(d)

Fair value measurements (Details)

v3.8.0.1
Fair value measurements (Details) - USD ($)
$ in Thousands
Mar. 31, 2018
Dec. 31, 2017
Marketable securities:    
Available-for-sale securities, Debt Securities, Current, Total $ 108,459 $ 124,218
Recurring basis    
Marketable securities:    
Corporate debt securities 99,465  
Government bonds 6,007  
Commercial paper 2,987  
Available-for-sale securities, Debt Securities, Current, Total 108,459  
Recurring basis | Level 1    
Marketable securities:    
Corporate debt securities 99,465  
Government bonds 6,007  
Available-for-sale securities, Debt Securities, Current, Total 105,472  
Recurring basis | Level 2    
Marketable securities:    
Commercial paper 2,987  
Available-for-sale securities, Debt Securities, Current, Total $ 2,987