Accounting policies - Performance obligations (Details) $ in Millions	6 Months Ended
	Jun. 30, 2025 USD ($)
Revenue remaining performance obligation expected timing of satisfaction
Amount recognized revenue included in the contract liability balance	$ 3.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-12-31
Revenue remaining performance obligation expected timing of satisfaction
Revenue remaining performance obligation, amount	$ 12.1
Revenue remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-12-31
Revenue remaining performance obligation expected timing of satisfaction
Revenue remaining performance obligation, amount	$ 143.1
Revenue remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-12-31
Revenue remaining performance obligation expected timing of satisfaction
Revenue remaining performance obligation, amount	$ 131.0
Revenue remaining performance obligation, expected timing of satisfaction, period	2 years