Common stock and convertible preferred stock - Preferred Stock (Details)	1 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) D $ / shares shares	Nov. 30, 2019 USD ($) shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares
Class of Stock [Line Items]
Gross proceeds			$ 11,046,000	$ 4,616,000
Payment of IPO costs			$ 49,000	$ 35,000
Convertible preferred stock
Class of Stock [Line Items]
Number of shares issued | shares	1,226,925		388,888	512,826
Issue price per share | $ / shares	$ 9.00		$ 9.00	$ 9.00
Gross proceeds	$ 11,000,000.0		$ 3,500,000	$ 4,600,000
Payment of IPO costs				$ 35,000
Shares issued for conversion of debt | shares		821,657	5,670,184
Amount of debt converted		$ 6,800,000
Shares purchased by issuing warrants | shares	1,035,196
Exercise price | $ / shares	$ 9.00
Warrants rights term	3 years
Stock price | $ / shares	$ 27.00
Number of trading days	10
Number of consecutive trading days | D	20
Fair value	$ 1,500,000