Net loss per share attributable to common stockholders - Antidilutive shares (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	31,672,608	30,584,103
Series A Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	2,151,641	2,151,641
Series B Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	5,886,405	5,886,405
Series C Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	11,473,110	11,473,110
Series D Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	7,034,423	7,034,423
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	4,947,296	3,852,087
Performance-based stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	21,459	28,163
Series D Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Amounts excluded from computation of diluted net loss per share	158,274	158,274