Commitments and Contingencies (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2013	Sep. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Guarantee Obligations [Line Items]
Lease expense for operating leases			$ 4,000,000	$ 3,900,000	$ 4,700,000
Additional bonding capacity			431,200,000
Proceeds from legal settlements	$ 1,700,000
Liquidated damages			5,400,000
Probable liquidated damages			1,800,000
Loss contingency, estimate of actual or projected loss			1,700,000
Facility Agreement | Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability			4,000,000
Revolving credit facility			15,200,000
Amount of credit facility remaining borrowing capacity			11,200,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability			21,100,000
Performance Guarantee
Guarantee Obligations [Line Items]
Guarantee liability			318,800,000
Acheson Alberta Canada
Guarantee Obligations [Line Items]
Loss on sublease and write-off of leasehold improvements			$ 800,000
Edmonton Alberta Canada
Guarantee Obligations [Line Items]
Loss on sublease and write-off of leasehold improvements		$ 1,700,000