Stock-based compensation - Stock option valuation assumptions (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Assumptions used in the Black-Scholes option-pricing model
Risk-free interest rate	4.12%	4.48%	4.52%	3.70%
Expected term (in years)	5 years 10 months 24 days	4 years 4 months 24 days	6 years	5 years 8 months
Expected volatility	103.00%	90.60%	101.50%	93.50%