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Subsequent Events - Additional Information (Detail)
$ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2015
USD ($)
Entity
Sep. 30, 2015
Entity
Jun. 30, 2015
Entity
Mar. 31, 2015
Entity
Sep. 30, 2015
USD ($)
Entity
Dec. 31, 2014
USD ($)
Entity
Subsequent Event [Line Items]            
Number of business acquisitions   4 3 3 10 9
Cash paid or payable | $         $ 98,941 $ 279,533
Electric Power Infrastructure Services Business [Member]            
Subsequent Event [Line Items]            
Number of business acquisitions         7  
Scenario Forecast [Member]            
Subsequent Event [Line Items]            
Cash paid or payable | $ $ 9,600          
Scenario Forecast [Member] | Electric Power Infrastructure Services Business [Member]            
Subsequent Event [Line Items]            
Number of business acquisitions 1