Commitments and Contingencies (Narrative) (Details)	3 Months Ended
	Dec. 31, 2016 USD ($)
Guarantee Obligations [Line Items]
Additional bonding capacity	$ 520,600,000
Liquidated damages	2,700,000
Probable liquidated damages	1,700,000
Loss contingency, estimate of actual or projected loss	1,500,000
Facility Agreement | Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability	4,800,000
Revolving credit facility	6,168,000
Amount of credit facility remaining borrowing capacity	1,400,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	20,300,000
Surety Bonds
Guarantee Obligations [Line Items]
Guarantee liability	$ 229,400,000