Annual report pursuant to Section 13 and 15(d)

Financial instruments - Fair value of assets and liabilities (Details)

v3.10.0.1
Financial instruments - Fair value of assets and liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2018
Dec. 31, 2017
Marketable securities:    
Marketable securities $ 136,755 $ 124,218
Recurring basis    
Marketable securities:    
Marketable securities 136,755  
Recurring basis | Level 1    
Marketable securities:    
Marketable securities 125,813  
Recurring basis | Level 2    
Marketable securities:    
Marketable securities 10,942  
Corporate debt securities | Recurring basis    
Marketable securities:    
Marketable securities 125,813 124,218
Corporate debt securities | Recurring basis | Level 1    
Marketable securities:    
Marketable securities 125,813 $ 124,218
Agency bond | Recurring basis    
Marketable securities:    
Marketable securities 3,965  
Agency bond | Recurring basis | Level 2    
Marketable securities:    
Marketable securities 3,965  
Treasury bills | Recurring basis    
Marketable securities:    
Marketable securities 1,980  
Treasury bills | Recurring basis | Level 2    
Marketable securities:    
Marketable securities 1,980  
Certificate of deposit | Recurring basis    
Marketable securities:    
Marketable securities 3,002  
Certificate of deposit | Recurring basis | Level 2    
Marketable securities:    
Marketable securities 3,002  
Commercial paper | Recurring basis    
Marketable securities:    
Marketable securities 1,995  
Commercial paper | Recurring basis | Level 2    
Marketable securities:    
Marketable securities $ 1,995