Common stock warrants - Warrants outstanding April 2020 (Details) - $ / shares	Dec. 31, 2023	Nov. 06, 2023	Dec. 31, 2022	Dec. 31, 2021
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	11,308,314		392,155	512,155
Exercise price of warrants (in dollars per share)	$ 1.09		$ 8.58	$ 8.62
July 2019 Series A warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	338,155
Exercise price of warrants (in dollars per share)	$ 8.75
July 2019 Series B warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)				120,000
Exercise price of warrants (in dollars per share)	$ 8.75
April 2020 Series A warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	44,000
Exercise price of warrants (in dollars per share)	$ 7.50
April 2020 Series B warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	10,000
Exercise price of warrants (in dollars per share)	$ 7.50
June 2023 pre-funded warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share)	$ 0.0001
June 2023 warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	1,427,587
Exercise price of warrants (in dollars per share)	$ 1.90
November 2023 Series A Warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	6,000,000
Exercise price of warrants (in dollars per share)	$ 0.70
November 2023 Series B Warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	3,000,000
Exercise price of warrants (in dollars per share)	$ 0.70
November 2023 Pre-Funded Warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares)	488,572
Exercise price of warrants (in dollars per share)	$ 0.0001	$ 0.0001