Net loss per share - Common share equivalents have been excluded from the calculation of diluted net loss per share (Details) - shares	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Stock options
Net loss per share
Number of common share equivalents excluded in the calculation of diluted net loss per share	2,185,706	2,428,268
Unvested restricted stock and stock units
Net loss per share
Number of common share equivalents excluded in the calculation of diluted net loss per share	587,939	563,810

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