Quarterly report pursuant to Section 13 or 15(d)

Acquisitions (Detail)

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Acquisitions (Detail) - USD ($)
$ in Thousands
1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2018
Jul. 20, 2017
Jan. 31, 2018
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Dec. 31, 2017
Business Acquisition [Line Items]                  
Contingent consideration, maximum $ 154,400     $ 154,400   $ 154,400   $ 154,400  
Net tangible assets acquired               107,700  
Other intangible assets acquired               116,600  
Goodwill acquired           43,181   344,200  
Revenues included in consolidated results of operations       2,656,348 $ 2,200,374 5,073,924 $ 4,378,544    
Income (loss) before taxes       104,095 $ 104,605 160,709 $ 175,637    
Electric Power Infrastructure Services Division                  
Business Acquisition [Line Items]                  
Goodwill acquired           43,181      
Oil and Gas Infrastructure Services Division                  
Business Acquisition [Line Items]                  
Goodwill acquired           0      
Acquisitions 2018                  
Business Acquisition [Line Items]                  
Cash consideration transferred or to be transferred 51,345   $ 51,300 12,100          
Number of shares granted for acquired companies (in shares)     379,817            
Value of Quanta common stock issued 13,549   $ 13,500            
Contingent consideration, maximum     $ 15,000            
Contingent consideration financial target term     5 years            
Contingent consideration, liability 13,705   $ 13,700 13,705   13,705   13,705  
Other intangible assets acquired           19,836      
Goodwill acquired 43,181                
Goodwill expected to be deductible for income tax 9,800     9,800   9,800   9,800  
Revenues included in consolidated results of operations       11,200   19,300      
Income (loss) before taxes       (1,300)   (6,600)      
Acquisition costs       (400)   (6,000)      
Acquisitions 2018 | Electric Power Infrastructure Services Division                  
Business Acquisition [Line Items]                  
Goodwill acquired           43,200      
Stronghold, Ltd. and Stronghold Specialty, Ltd.                  
Business Acquisition [Line Items]                  
Cash consideration transferred or to be transferred 351,014 $ 351,000              
Number of shares granted for acquired companies (in shares)   2,693,680              
Value of Quanta common stock issued 81,337 $ 81,300              
Contingent consideration, maximum   $ 100,000              
Contingent consideration financial target term   3 years              
Contingent consideration, liability 51,084 $ 51,100   51,084   51,084   51,084  
Goodwill acquired 296,542                
Stronghold, Ltd. and Stronghold Specialty, Ltd. | Oil and Gas Infrastructure Services Division                  
Business Acquisition [Line Items]                  
Goodwill acquired                 $ 296,500
Acquisitions 2017, other than Stronghold                  
Business Acquisition [Line Items]                  
Cash consideration transferred or to be transferred 11,955               $ 12,000
Number of shares granted for acquired companies (in shares)                 288,666
Value of Quanta common stock issued 8,267               $ 8,300
Contingent consideration, liability 0     $ 0   $ 0   $ 0  
Goodwill acquired $ 5,917                
Acquisitions 2017, other than Stronghold | Electric Power Infrastructure Services Division                  
Business Acquisition [Line Items]                  
Goodwill acquired                 5,900
Acquisitions 2017                  
Business Acquisition [Line Items]                  
Goodwill expected to be deductible for income tax                 $ 302,500