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Commitments and Contingencies (Concentrations of Credit Risk) - Additional Information (Detail)

v3.7.0.1
Commitments and Contingencies (Concentrations of Credit Risk) - Additional Information (Detail)
$ in Thousands
3 Months Ended
Dec. 31, 2016
USD ($)
Customer
Mar. 31, 2017
USD ($)
Customer
Concentration Risk [Line Items]    
Costs and estimated earnings in excess of billings on uncompleted contracts $ 473,308 $ 556,527
Customer Concentration Risk [Member]    
Concentration Risk [Line Items]    
Net position balance $ 277,300 $ 300,400
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% 16.00%
Costs and estimated earnings in excess of billings on uncompleted contracts $ 175,900 $ 191,100
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Oil and Gas Infrastructure Services Segment [Member]    
Concentration Risk [Line Items]    
Number of customers representing ten percent or more of concentration risk | Customer   2