Summary of significant accounting policies - Potentially dilutive securities (Details) - shares	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Potentially dilutive securities
Total shares of common stock equivalents	5,118,834	3,771,459
Options to purchase common stock
Potentially dilutive securities
Total shares of common stock equivalents	4,719,115	3,771,459
Restricted stock units
Potentially dilutive securities
Total shares of common stock equivalents	399,719

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

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