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Commitments and Contingencies (Concentrations of Credit Risk) - Additional Information (Detail)
$ in Thousands
12 Months Ended
Dec. 31, 2016
USD ($)
Customer
Dec. 31, 2015
USD ($)
Customer
Dec. 31, 2014
Customer
Concentration Risk [Line Items]      
Costs and estimated earnings in excess of billings on uncompleted contracts $ 473,308 $ 317,745  
Customer Concentration Risk [Member]      
Concentration Risk [Line Items]      
Net position balance $ 277,300 $ 195,200  
Net Receivable Position [Member] | Customer Concentration Risk [Member] | Quanta's Electric Power Infrastructure Services Segment [Member]      
Concentration Risk [Line Items]      
Number of customers representing ten percent or more of concentration risk | Customer 1 1  
Concentration risk percentage 16.00% 12.00%  
Costs and estimated earnings in excess of billings on uncompleted contracts $ 175,900 $ 83,900  
Sales Revenue, Net [Member] | Customer Concentration Risk [Member]      
Concentration Risk [Line Items]      
Number of customers representing ten percent or more of concentration risk | Customer 0 0 0