Commitments and Contingencies (Details) $ in Millions	6 Months Ended
Mar. 31, 2025 USD ($)
Guarantee Obligations [Line Items]
Additional bonding capacity	$ 779.7
Cash collateral required for guarantees, period (greater than)	2 years
Contracts with probable exposure to liquidated damages	$ 2.7
Probable exposure potential increase	3.6
Change in contract estimates, reduction to revenue	2.5
Surety Bonds
Guarantee Obligations [Line Items]
Guarantee liability	420.3
Facility Agreement \| Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability	4.0
Revolving credit facility	19.4
Amount of credit facility remaining borrowing capacity	15.4
Revolving Credit Facility \| U.S. Revolver
Guarantee Obligations [Line Items]
Amount of credit facility remaining borrowing capacity	85.6
Revolving Credit Facility \| U.S. Revolver \| Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	$ 64.4

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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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