Annual report pursuant to Section 13 and 15(d)

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

v3.19.3.a.u2
Financial instruments - Fair value of assets and liabilities (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Marketable securities:    
Marketable securities $ 39,130 $ 136,755
Recurring basis    
Marketable securities:    
Marketable securities 39,130 136,755
Recurring basis | Level 1    
Marketable securities:    
Marketable securities 39,130 125,813
Recurring basis | Level 2    
Marketable securities:    
Marketable securities   10,942
Corporate debt securities | Recurring basis    
Marketable securities:    
Marketable securities 39,130 125,813
Corporate debt securities | Recurring basis | Level 1    
Marketable securities:    
Marketable securities $ 39,130 125,813
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