Stock-based compensation - Stock Options and RSUs (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Employee stock options
Number of Shares
Beginning Balance (in shares) | shares	2,598,745
Granted (in shares) | shares	0
Exercised/Converted (in shares) | shares	(52,501)
Cancelled/Forfeited (in shares) | shares	(23,505)
Ending Balance (in shares) | shares	2,522,739
Weighted Average Exercise Price
Beginning Balance (in USD per share) | $ / shares	$ 5.93
Granted (in USD per share) | $ / shares	0
Exercised/Converted (in USD per share) | $ / shares	4.40
Cancelled/Forfeited (in USD per share) | $ / shares	11.15
Ending Balance (in USD per share) | $ / shares	$ 5.91
Restricted stock units
Number of Units
Beginning Balance (in shares) | shares	3,170,981
Granted (in shares) | shares	224,131
Exercised/Converted (in shares) | shares	(114,188)
Cancelled/Forfeited (in shares) | shares	(61,675)
Ending Balance (in shares) | shares	3,219,249
Weighted Average Exercise Price
Beginning Balance (in USD per share) | $ / shares	$ 5.80
Granted (in USD per share) | $ / shares	6.72
Exercised/Converted (in USD per share) | $ / shares	5.96
Cancelled/Forfeited (in USD per share) | $ / shares	6.10
Ending Balance (in USD per share) | $ / shares	$ 5.85