Commitments and Contingencies (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2013	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Guarantee Obligations [Line Items]
Lease expense for operating leases			$ 3,900,000	$ 4,700,000	$ 4,300,000
Loss on sublease and write-off of leasehold improvements		1,700,000
Additional bonding capacity			301,300,000
Proceeds from legal settlements	1,700,000
Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability			2,600,000
Revolving credit facility			16,200,000
Amount of credit facility remaining borrowing capacity			13,600,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability			21,500,000
Performance Guarantee
Guarantee Obligations [Line Items]
Guarantee liability			$ 298,700,000