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Equity - Additional Information (Detail) (USD $)
 0 Months Ended 3 Months Ended 9 Months Ended
Mar. 31, 2013
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Dec. 31, 2013
Equity [Line Items]            
Minimum number of shares that can be exchanged by exchangeable shareholders unless the number of remaining exchangeable shares registered in the name of the holder is less       50,000    
Number of shares of Common stock received for each exchangeable share       1    
Exchangeable shares exchanged for common stock 409,110          
Shares outstanding   212,462,599   212,462,599   212,942,767
Aggregate authorized amount of common stock to be repurchased   $ 500,000,000   $ 500,000,000    
Reduction in net income as a result of non controlling interests   5,367,000 5,503,000 13,969,000 14,768,000  
Carrying value of the investments held by Quanta in variable interest entities   17,600,000   17,600,000   7,100,000
Distributions to non-controlling interests   3,000,000 2,500,000 3,500,000 11,800,000  
Carrying value of the investment held by noncontrolling interest in variable interest entities   17,594,000   17,594,000   7,131,000
Treasury Stock [Member]
            
Equity [Line Items]            
Treasury stock acquired   0   1,300,000    
Value of treasury stock acquired, cost method       45,000,000    
Series F Preferred Stock [Member]
            
Equity [Line Items]            
Number of preferred Stock issued to voting trust   1   1    
Series G Preferred Stock [Member]
            
Equity [Line Items]            
Number of preferred Stock issued to voting trust   1   1    
Exchangeable Shares [Member]
            
Equity [Line Items]            
Shares outstanding   5,221,377   5,221,377   3,500,000
Exchangeable Shares Not Associated With Preferred Stock [Member]
            
Equity [Line Items]            
Shares outstanding   4,399,858   4,399,858    
Common Stock Withheld for Settlement of Employee Tax Liabilities [Member] | Treasury Stock [Member]
            
Equity [Line Items]            
Treasury stock acquired       300,000 400,000  
Value of treasury stock acquired, cost method       $ 11,900,000 $ 12,000,000