Stockholders' equity (Details)		12 Months Ended
	Nov. 12, 2020 USD ($)	Dec. 31, 2021 USD ($) Vote $ / shares shares	Dec. 31, 2020 $ / shares shares	Dec. 31, 2019 $ / shares shares	Sep. 30, 2019 $ / shares
Stockholders' equity
Stock, shares authorized		440,000,000
Common stock, shares authorized		400,000,000	400,000,000	400,000,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.001	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized		40,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.001
Number of shares issued		366,773	0
Commission payable as a percentage of gross proceeds from sale of common stock under ATM offering	3.00%
Proceeds from at-the-market sales of common stock, net | $		$ 1,538,645
Common stock, shares outstanding		21,859,413	21,186,827
Number of voting rights per common share | Vote		1
Shelf Registration Statement
Maximum amount to be issued under universal shelf registration statement | $	$ 350,000,000.0
Maximum amount to be issued under at-the-market offering program | $	$ 50,000,000.0