COMMITMENTS AND CONTINGENCIES (Details)	9 Months Ended
	Jun. 30, 2017 USD ($)
Guarantee Obligations [Line Items]
Additional bonding capacity	$ 528,300,000
Liquidated damages	6,800,000
Probable liquidated damages	1,500,000
Loss contingency, estimate of actual or projected loss	1,500,000
Facility Agreement | Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability	4,200,000
Revolving credit facility	6,500,000
Amount of credit facility remaining borrowing capacity	2,300,000
Surety Bonds
Guarantee Obligations [Line Items]
Guarantee liability	221,700,000
U.S. Revolver
Guarantee Obligations [Line Items]
Revolving credit facility	75,000,000.0
Amount of credit facility remaining borrowing capacity	50,400,000
U.S. Revolver | Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	$ 24,600,000