Earnings per share - Schedule of Earnings Per Share, Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net earnings	$ 32.4	$ 40.0	$ 34.3	$ 89.0
Weighted average number of shares outstanding, basic (in shares)	71.8	71.5	71.7	71.4
Basic net (loss)/earnings per common share (in dollars per share)	$ 0.45	$ 0.56	$ 0.48	$ 1.25
Weighted average number of shares outstanding, diluted (in shares)	72.6	72.4	72.6	72.3
Diluted net (loss)/earnings per common share- continuing operations (in dollars per share)	$ 0.45	$ 0.55	$ 0.47	$ 1.23
Restricted Stock Equivalents
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0.5	0.1	0.5	0.2
Performance Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1.3	1.3	1.3	1.3
Deferred Compensation, Share-based Payments
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Effect of dilutive performance shares (shares)	0.0	0.0	0.0	0.1
Retained (Losses)/Earnings
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net earnings	$ 32.4
Performance Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Effect of dilutive performance shares (shares)	0.5	0.5	0.5	0.5
Restricted Stock Equivalents
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Effect of dilutive performance shares (shares)	0.3	0.4	0.4	0.3