Shareholders' equity (Details) € / shares in Units, $ in Thousands				3 Months Ended
	Apr. 07, 2025 USD ($) shares	Apr. 07, 2025 EUR (€) € / shares shares	Mar. 27, 2025 EUR (€) session € / shares shares	Sep. 30, 2025 USD ($) shares	Jun. 30, 2025 USD ($)	Mar. 31, 2025 USD ($)	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2025 EUR (€) € / shares shares	Jun. 11, 2025 EUR (€)	Apr. 06, 2025 EUR (€) shares	Dec. 31, 2024 € / shares	Dec. 31, 2024 USD ($) shares
Class of Stock [Line Items]
Common stock, value, issued		€ 13,694,887.2		$ 15,394						€ 13,697,516		€ 10,285,886.8		$ 11,651
Common stock, shares oustanding (in shares) | shares				136,975,159						136,975,159
Common stock shares par value (in Euro per share)		€ 0.10								€ 0.1			€ 0.1
Accumulated deficit				$ 348,301							€ 102,284,799.3			$ 286,375
Capital increase authorized, maximum nominal amount | €			€ 28,929,000
Number of consecutive trading session | session			5
Number of total trading session | session			30
Volume average price			€ 0.8989
Discount rate for exercise price			15.00%
Discounted volume average price			€ 0.7641
Issuance of ordinary shares | $				$ 0	$ 30,982	$ 0	$ 0	$ 0	$ 0
Common stock shares issued (in shares) | shares		136,948,872		136,975,159						136,975,159		102,858,868		102,847,501
ABSA warrants
Class of Stock [Line Items]
Warrant shares to warrants, ratio			1.75
Class of warrant or right, exercise price of warrants or rights (in euro per share)		€ 1.1136	€ 1.5939
Stock issued during period (in shares) | shares	34,090,004	34,090,004
Shares issued (in USD/Euro per share)		€ 0.10
Issuance of ordinary shares	$ 42,000	€ 38,000,000
Prefunded PFW-BS-PFW
Class of Stock [Line Items]
Class of warrant or right, unissued (in shares) | shares		1	1
Class of warrant or right, exercise price of warrants or rights (in euro per share)		€ 1.1036
First prefunded warrants
Class of Stock [Line Items]
Class of warrant or right, number of securities called by each warrant or right (in shares) | shares		1	1	1						1
Class of warrant or right, exercise price of warrants or rights (in euro per share)			€ 0.01
BS Warrants
Class of Stock [Line Items]
Class of warrant or right, unissued (in shares) | shares		1	1
Second prefunded warrants
Class of Stock [Line Items]
Warrant shares to warrants, ratio		1.75	1.75	1.75						1.75
Class of warrant or right, number of securities called by each warrant or right (in shares) | shares		1	1
ABSA
Class of Stock [Line Items]
Class of warrant or right, exercise price of warrants or rights (in euro per share)			€ 1.1136
Share issuance premium, percentage			23.89%
Stock issued during period (in shares) | shares			34,090,004
Shares issued (in USD/Euro per share)			€ 0.10
Exercise price of issue premium (in euro per share)			€ 1.0136
Issuance of ordinary shares | €			€ 3,409,000.4
PFW-BS-PFW
Class of Stock [Line Items]
Class of warrant or right, exercise price of warrants or rights (in euro per share)		€ 1.1136	€ 1.1136
Stock issued during period (in shares) | shares	71,005,656	71,005,656	71,005,656
Issuance of ordinary shares	$ 86,000	€ 79,000,000