Stock-based compensation - Schedule of Stock Options Outstanding and Exercisable (Details)	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options outstanding (in shares) | shares	24,959,807
Options exercisable (in shares) | shares	8,844,727
Exercise Price at $0.13
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	$ 0.18
Exercise price, upper range limit (in dollars per share)	$ 0.18
Options outstanding (in shares) | shares	6,350,481
Options outstanding, weighted average remaining contractual life (years)	8 years 3 months 18 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.18
Options exercisable (in shares) | shares	3,889,338
Options exercisable, weighted average remaining contractual life (years)	7 years 9 months 18 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.18
Exercise Price at $0.15
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	0.21
Exercise price, upper range limit (in dollars per share)	$ 0.21
Options outstanding (in shares) | shares	10,394,961
Options outstanding, weighted average remaining contractual life (years)	8 years 9 months 18 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.21
Options exercisable (in shares) | shares	3,186,660
Options exercisable, weighted average remaining contractual life (years)	8 years 2 months 12 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.21
Exercise Price at $0.26
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	0.37
Exercise price, upper range limit (in dollars per share)	$ 0.37
Options outstanding (in shares) | shares	35,159
Options outstanding, weighted average remaining contractual life (years)	4 months 24 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 0.37
Options exercisable (in shares) | shares	35,159
Options exercisable, weighted average remaining contractual life (years)	4 months 24 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 0.37
Exercise Price at $1.00
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	1.42
Exercise price, upper range limit (in dollars per share)	$ 1.42
Options outstanding (in shares) | shares	7,524,116
Options outstanding, weighted average remaining contractual life (years)	9 years
Options outstanding, weighted average exercise price (in dollars per share)	$ 1.42
Options exercisable (in shares) | shares	1,724,276
Options exercisable, weighted average remaining contractual life (years)	9 years
Options exercisable, weighted average exercise price (in dollars per share)	$ 1.42
Exercise Price at $3.92
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	5.57
Exercise price, upper range limit (in dollars per share)	$ 5.57
Options outstanding (in shares) | shares	7,976
Options outstanding, weighted average remaining contractual life (years)	2 months 12 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.57
Options exercisable (in shares) | shares	7,976
Options exercisable, weighted average remaining contractual life (years)	2 months 12 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 5.57
Exercise Price at $5.80
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	8.25
Exercise price, upper range limit (in dollars per share)	$ 8.25
Options outstanding (in shares) | shares	1,318
Options outstanding, weighted average remaining contractual life (years)	2 months 12 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 8.25
Options exercisable (in shares) | shares	1,318
Options exercisable, weighted average remaining contractual life (years)	2 months 12 days
Options exercisable, weighted average exercise price (in dollars per share)	$ 8.25
Exercise Price at $10.26
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower range limit (in dollars per share)	10.26
Exercise price, upper range limit (in dollars per share)	$ 10.26
Options outstanding (in shares) | shares	645,796
Options outstanding, weighted average remaining contractual life (years)	9 years 6 months
Options outstanding, weighted average exercise price (in dollars per share)	$ 10.26
Options exercisable (in shares) | shares	0
Options exercisable, weighted average exercise price (in dollars per share)	$ 0