Quarterly report pursuant to Section 13 or 15(d)

Equity (Details Textual)

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Equity (Details Textual) (USD $)
 3 Months Ended 5 Months Ended 6 Months Ended
Jun. 30, 2012
Mar. 31, 2012
Jun. 30, 2011
Aug. 31, 2011
Jun. 30, 2012
Jun. 30, 2011
Dec. 31, 2011
Equity (Textual) [Abstract]              
Aggregate authorized amount of common stock to be repurchased       $ 150,000,000      
Number of shares of Common stock received for each exchangeable share         1    
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    
Reduction in net income as a result of non controlling interests 4,259,000   2,512,000   8,546,000 3,801,000  
Carrying value of the investments held by Quanta in variable interest entities 9,600,000       9,600,000   7,300,000
Carrying value of the investment held by noncontrolling interest in variable interest entities 9,620,000       9,620,000   7,311,000
Distributions to noncontrolling interests   3,700,000 500,000   6,200,000 500,000  
Treasury Stock [Member]
              
Equity (Additional Textual) [Abstract]              
Value of treasury stock acquired, cost method       149,500,000      
Common Stock Withheld for Settlement of Employee Tax Liabilities [Member]
              
Equity (Additional Textual) [Abstract]              
Treasury stock acquired         286,954 277,923  
Value of treasury stock acquired, cost method         $ 6,100,000 $ 6,200,000  
Common Stock [Member]
              
Equity (Additional Textual) [Abstract]              
Treasury stock acquired       8,100,000      
Series F Preferred Stock [Member]
              
Equity (Additional Textual) [Abstract]              
Number of preferred Stock issued to voting trust 1       1