Commitments and Contingencies (Details) - USD ($) $ in Millions	9 Months Ended
Jun. 30, 2024	Jun. 30, 2023
Guarantee Obligations [Line Items]
Additional bonding capacity	$ 777.9
Cash collateral required for guarantees, period (greater than)	2 years
Contracts with probable exposure to liquidated damages	$ 2.5
Probable exposure potential increase	2.8
Change in contract estimates, reduction to revenue	1.7	$ 3.4
Surety Bonds
Guarantee Obligations [Line Items]
Guarantee liability	422.1
Facility Agreement \| Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability	6.4
Revolving credit facility	19.0
Amount of credit facility remaining borrowing capacity	12.6
Revolving Credit Facility \| U.S. Revolver
Guarantee Obligations [Line Items]
Amount of credit facility remaining borrowing capacity	81.6
Revolving Credit Facility \| U.S. Revolver \| Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	$ 68.4

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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