Summary of significant accounting policies - Net loss per share (Details) - shares	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Potentially dilutive securities
Total shares of common stock equivalents	6,203,941	5,294,236
Options to purchase common stock
Potentially dilutive securities
Total shares of common stock equivalents	5,745,621	4,794,236
Restricted stock units
Potentially dilutive securities
Total shares of common stock equivalents	458,320	500,000

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration