Income taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Income taxes
Income tax expense	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Uncertain tax positions	$ 0.1		$ 0.1		$ 0.1

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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+ Details