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Stockholders' equity - Summary of options outstanding and exercisable (Details)
3 Months Ended
Mar. 31, 2020
$ / shares
shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of options outstanding (in shares) 657,548
Number of options exercisable (in shares) 524,398
Weighted average exercise price of outstanding and exercisable options (in dollars per share) | $ / shares $ 4.93
$1.88 - $2.50  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of options outstanding (in shares) 525,519
Weighted average remaining estimated life (in years) 9 years
Number of options exercisable (in shares) 392,369
$3.30 - $6.90  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of options outstanding (in shares) 37,139
Weighted average remaining estimated life (in years) 2 years 3 months 18 days
Number of options exercisable (in shares) 37,139
$7.50 - $10.80  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of options outstanding (in shares) 21,303
Weighted average remaining estimated life (in years) 4 years 1 month 6 days
Number of options exercisable (in shares) 21,303
$14.20 - $23.40  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Number of options outstanding (in shares) 73,587
Weighted average remaining estimated life (in years) 6 years 1 month 6 days
Number of options exercisable (in shares) 73,587
Minimum | $1.88 - $2.50  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares $ 1.88
Minimum | $3.30 - $6.90  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares 3.30
Minimum | $7.50 - $10.80  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares 7.50
Minimum | $14.20 - $23.40  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares 14.20
Maximum | $1.88 - $2.50  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares 2.50
Maximum | $3.30 - $6.90  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares 6.90
Maximum | $7.50 - $10.80  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares 10.80
Maximum | $14.20 - $23.40  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Weighted average price of outstanding options (in dollars per share) | $ / shares $ 23.40