Accounting policies - Performance obligations (Details) $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($)
Revenue remaining performance obligation expected timing of satisfaction
Amount recognized revenue included in the contract liability balance	$ 5.1
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	$ 4.6
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	$ 138.8
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	$ 134.2
Revenue remaining performance obligation, expected timing of satisfaction, period	2 years