Stockholders' equity - Schedule of RSU Activity (Details) - Restricted stock units	12 Months Ended
	Dec. 31, 2020 $ / shares shares
RSU Activity
Non-vested beginning balance (in shares) | shares	72,000
Restricted stock units granted (in shares) | shares	152,000
Restricted stock units vested (in shares) | shares	(36,000)
Restricted stock units forfeited (in shares) | shares	(1,500)
Non-vested ending balance (in shares) | shares	186,500
RSU Activity Weighted Average Grant Date Fair Value
Non-vested beginning balance (in dollars per share) | $ / shares	$ 3.47
Restricted stock units granted (in dollars per share) | $ / shares	9.26
Restricted stock units vested (in dollars per share) | $ / shares	3.47
Restricted stock units forfeited (in dollars per share) | $ / shares	3.47
Non-vested ending balance (in dollars per share) | $ / shares	$ 8.19