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Stock-based compensation - Summary of Activity for Options Vest Solely Based upon Satisfaction of Service Condition (Details) - Service-based Stock Options
$ / shares in Units, $ in Thousands
 3 Months Ended
Mar. 31, 2018
USD ($)
$ / shares
shares
Options outstanding  
Beginning balance (in shares) | shares 2,597,294
Granted (in shares) | shares 585,250
Exercised (in shares) | shares (28,463)
Forfeited (in shares) | shares (72,505)
Canceled (in shares) | shares (30,032)
Ending balance (in shares) | shares 3,051,544
Options outstanding, Exercisable (in shares) | shares 1,326,527
Weighted-average exercise price  
Beginning balance (in USD per share) | $ / shares $ 10.66
Granted (in USD per share) | $ / shares 18.43
Exercised (in USD per share) | $ / shares 5.66
Forfeited (in USD per share) | $ / shares 6.45
Canceled (in USD per share) | $ / shares 4.60
Ending balance (in USD per share) | $ / shares 12.35
Weighted-average exercise price, Exercisable (in USD per share) | $ / shares $ 6.89
Weighted-average remaining contractual life (in years), Outstanding 8 years 1 month 6 days
Weighted-average remaining contractual life(in years), Exercisable 6 years 10 months 24 days
Aggregate intrinsic values, Outstanding | $ $ 22,479
Aggregate intrinsic values, Exercisable | $ $ 16,797