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Employee Benefit Plans - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Employee Benefit Plans [Line Items]      
Partial withdrawal liability     $ 32.6
Multiemployer defined contribution and other benefit plan contributions other than MEP DBP 104.4 87.0 46.7
401K Plan [Member]
      
Employee Benefit Plans [Line Items]      
Percentage of contribution by employer of each employee's contribution up to 3% 100.00%    
Percentage of contribution by employer of each employee who contributes between three and six percent 50.00%    
Percentage of employee contribution, lower range 3.00%    
Percentage of employee contribution, high range 6.00%    
Quanta 401(k) Plan, Contributions to non-union defined contribution plans $ 11.8 $ 11.0 $ 9.5
Red Zone [Member]
      
Employee Benefit Plans [Line Items]      
Percentage Funded in this Zone Less than 65%    
Yellow Zone [Member]
      
Employee Benefit Plans [Line Items]      
Percentage Funded in this Zone Less than 80%    
Green Zone [Member]
      
Employee Benefit Plans [Line Items]      
Percentage Funded in this Zone at least 80%