Commitments and Contingencies - Narrative (Details)	12 Months Ended
	Sep. 30, 2022 USD ($)
Guarantor Obligations [Line Items]
Additional bonding capacity	$ 359,000,000
Cash collateral requirement for guarantees	2 years
Loss contingency, estimate of actual or projected loss	$ 3,500,000
Probable liquidated damages	2,200,000
Failure to meet contractual commitments, reduction to revenue	1,400,000
Facility Agreement | Powell (UK) Limited
Guarantor Obligations [Line Items]
Guarantee liability, letters of credit	3,100,000
Revolving credit facility	5,600,000
Amount of credit facility remaining borrowing capacity	2,500,000
Surety Bond
Guarantor Obligations [Line Items]
Guarantee liability, letters of credit	241,000,000
U.S. Revolver | Amended And Restated Credit Agreement
Guarantor Obligations [Line Items]
Revolving credit facility	75,000,000
Amount of credit facility remaining borrowing capacity	38,300,000
U.S. Revolver | Financial Standby Letter of Credit | Amended And Restated Credit Agreement
Guarantor Obligations [Line Items]
Guarantee liability, letters of credit	$ 36,700,000