Accounting policies - Performance obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 31, 2024
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Amount recognized revenue included in the contract liability balance	$ 2.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-12-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount		$ 15.0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-12-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount		$ 152.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-12-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount		$ 137.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period		2 years