Common stock and convertible preferred stock - Warrants (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares
Class of Warrant or Right [Line Items]
Gross proceeds from issuance of warrants | $	$ 1.3
Warrants
Class of Warrant or Right [Line Items]
Warrant liability | $	$ 7.1
Warrants exercised, numbers	148,653
Exercise price | $ / shares	$ 9.00
Exercise of common stock warrants (shares)	148,653
Additional warrants exercised on cashless	72,320
Additional warrants exercise price | $ / shares	$ 9.00
Shares issued in cashless exercise	45,322
Warrants | Exercise Price $9.00
Class of Warrant or Right [Line Items]
Warrants outstanding	814,223
Exercise price | $ / shares	$ 9.00
Warrants | Exercise Price $45.00
Class of Warrant or Right [Line Items]
Warrants outstanding	500,000
Exercise price | $ / shares	$ 45.00