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Stock-based compensation - Employee stock purchase plan (Details) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 21, 2019 item	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)
Assumptions used to estimate fair value of each stock-based award on the grant date
Stock-based compensation expense		$ 3,430	$ 3,413
Proceeds from the exercise of stock options and employee stock purchase program				$ 68	$ 22
Employee stock purchase plan
Stock-based compensation
Percent of common stock at market price to be purchased	85.00%
Number of vesting periods \| item	2
Vesting period	6 months
Assumptions used to estimate fair value of each stock-based award on the grant date
Risk-free interest rate (as a percent)				3.58%	4.25%
Volatility (as a percent)				84.00%	107.00%
Dividend yield (as a percent)				0.00%	0.00%
Expected term (years)				6 months	6 months
Stock-based compensation expense				$ 100	$ 100
Employee stock purchase plan \| Maximum
Assumptions used to estimate fair value of each stock-based award on the grant date
Proceeds from the exercise of stock options and employee stock purchase program				$ 100