Summary of significant accounting policies - Potentially dilutive securities (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Potentially dilutive securities
Total shares of common stock equivalents	648,448	521,120	249,293
Convertible preferred stock (as converted)
Potentially dilutive securities
Total shares of common stock equivalents	28,112	28,112
Employee Stock Option [Member]
Potentially dilutive securities
Total shares of common stock equivalents	596,466	480,274	229,308
Unvested restricted stock units
Potentially dilutive securities
Total shares of common stock equivalents	23,870	12,734	19,985