Commitments and Contingencies (Narrative) (Details) - Jun. 30, 2015 - USD ($)	Total
Guarantee Obligations [Line Items]
Additional bonding capacity	$ 446,800,000
Liquidated damages	6,700,000
Probable liquidated damages	2,000,000
Loss contingency, estimate of actual or projected loss	800,000
Powell (UK) Limited
Guarantee Obligations [Line Items]
Guarantee liability	6,400,000
Revolving credit facility	15,700,000
Amount of credit facility remaining borrowing capacity	9,300,000
Financial Standby Letter of Credit
Guarantee Obligations [Line Items]
Guarantee liability	18,100,000
Performance Guarantee
Guarantee Obligations [Line Items]
Guarantee liability	$ 303,200,000