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Business and Organization - Additional Information (Detail) (USD $)
 1 Months Ended 3 Months Ended 6 Months Ended 9 Months Ended 12 Months Ended 3 Months Ended 6 Months Ended 3 Months Ended 1 Months Ended 6 Months Ended 3 Months Ended 6 Months Ended
Jul. 31, 2013
Entity
Sep. 30, 2013
Sep. 30, 2012
Jun. 30, 2012
Entity
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Dec. 31, 2013
Subsequent Event [Member]
Entity
Jun. 30, 2012
Natural Gas and Pipeline Division [Member]
United States [Member]
Entity
Dec. 31, 2013
Natural Gas and Pipeline Division [Member]
United States [Member]
Subsequent Event [Member]
Entity
Jul. 31, 2013
Natural Gas and Pipeline Division [Member]
Australia [Member]
Entity
Jul. 31, 2013
Electric Power Division [Member]
United States [Member]
Entity
Jun. 30, 2012
Electric Power Division [Member]
United States [Member]
Entity
Dec. 31, 2013
Electric Power Division [Member]
United States [Member]
Subsequent Event [Member]
Entity
Jun. 30, 2012
Electric Power Division [Member]
Canada [Member]
Entity
Organization And Description Of Business [Line Items]                              
Fiber Optic Licensing Terms, Minimum in years   5 years 5 years   5 years 5 years 5 years                
Fiber Optic Licensing Terms, Maximum in years   25 years 25 years   25 years 25 years 25 years                
Number of business acquisitions completed 2     4       3 1 2 1 1 2 1 1
Cash paid for acquisition       $ 57,500,000       $ 180,800,000              
Common stock value 18,700,000     37,300,000       69,300,000              
Number of shares issued for acquisition of company 763,272     1,927,113       2,747,412              
Cash paid for acquisitions, net of cash acquired 123,800,000 123,759,000     124,736,000 68,727,000                  
Payment of cash to repay acquiree debt       11,000,000                      
Proceeds from sale of subsidiary             $ 265,000,000