Loss per share - Schedule of EPS (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Total net income (loss)	$ 56.5	$ (30.7)	$ (88.4)	$ (99.0)
Weighted average number of common shares (in shares)	23.2	22.3	23.2	22.2
Effect of dilutive securities:
Dilutive number of shares (in shares)	26.2	22.3	23.2	22.2
Profit (loss) per common share - basic (in dollars per share)	$ 2.15	$ (1.38)	$ (3.81)	$ (4.47)
Profit (loss) per common share - diluted (in dollars per share)	$ 2.43	$ (1.38)	$ (3.81)	$ (4.47)
Stock options
Effect of dilutive securities:
Effect of dilutive securities, Stock options and Restricted share units (in shares)	0.0	0.0	0.0	0.0
Restricted share units
Effect of dilutive securities:
Effect of dilutive securities, Stock options and Restricted share units (in shares)	3.0	0.0	0.0	0.0