Common stock and convertible preferred stock - Warrants (Details) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($) $ / shares shares
Class of Warrant or Right [Line Items]
Gross proceeds from issuance of warrants | $	$ 0.9
Warrants
Class of Warrant or Right [Line Items]
Warrant liability | $	$ 7.1
Warrants exercised, numbers	100,695
Exercise of common stock warrants (shares)	100,695
Additional warrants exercised on cashless	72,320
Shares issued in cashless exercise	45,322
Warrants | Exercise Price $9.00
Class of Warrant or Right [Line Items]
Warrants outstanding	862,181
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