Stock-based compensation - Restricted Stock - (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Restricted stock disclosures
Stock-based compensation.	$ 2,490	$ 3,991	$ 4,809	$ 7,592
Unvested restricted common stock units
Shares
Balance, beginning (in shares)			806,379
Granted (in shares)			739,080
Vested (in shares)			(344,255)
Forfeited (in shares)			(169,839)
Balance, ending (in shares)	1,031,365		1,031,365
Weighted Average Grant Date Fair Value Per Share
Balance, beginning (in dollars per share)			$ 7.26
Granted (in dollars per share)			3.79
Vested (in dollars per share)			7.45
Forfeited (in dollars per share)			5.06
Balance, ending (in dollars per share)	$ 5.08		$ 5.08
Restricted stock disclosures
Vesting period			3 years
Stock-based compensation.	$ 842	$ 1,392	$ 1,634	$ 2,366
Unrecognized stock-based compensation expense	$ 4,000		$ 4,000
Remaining weighted-average remaining vesting period			2 years
Minimum | Unvested restricted common stock units
Restricted stock disclosures
Vesting period	3 years
Maximum | Unvested restricted common stock units
Restricted stock disclosures
Vesting period	4 years