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Business And Organization (Narrative) (Detail)
 3 Months Ended 9 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2012
Entity
Sep. 30, 2011
Entity
Sep. 30, 2012
Sep. 30, 2011
Dec. 31, 2011
Entity
Jun. 30, 2012
Electric Power Division [Member]
United States [Member]
Entity
Mar. 31, 2012
Electric Power Division [Member]
United States [Member]
Entity
Dec. 31, 2011
Electric Power Division [Member]
United States [Member]
Entity
Mar. 31, 2012
Electric Power Division [Member]
Canada [Member]
Entity
Sep. 30, 2011
Electric Power Division [Member]
Canada [Member]
Entity
Dec. 31, 2011
Electric Power Division [Member]
Canada [Member]
Entity
Mar. 31, 2012
Natural Gas And Pipeline Division [Member]
United States [Member]
Entity
Sep. 30, 2011
Natural Gas And Pipeline Division [Member]
Australia [Member]
Entity
Dec. 31, 2011
Natural Gas And Pipeline Division [Member]
Australia [Member]
Entity
Business Acquisition [Line Items]                            
Fiber Optic Licensing Terms, Minimum in years     5 years 5 years                    
Fiber Optic Licensing Terms, Maximum in years     25 years 25 years                    
Number of business acquisitions completed 3 4     5 1 1 1 1 3 3 1 1 1