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Equity - Additional Information (Detail) (USD $)
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1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 12 Months Ended | |||||||
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Aug. 31, 2011
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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May 31, 2011
Limited Vote Common Stock [Member]
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Dec. 31, 2011
Limited Vote Common Stock [Member]
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Dec. 31, 2010
Limited Vote Common Stock [Member]
Vote
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Aug. 31, 2011
Common Stock [Member]
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Dec. 31, 2011
Common Stock [Member]
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Dec. 31, 2010
Common Stock [Member]
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Dec. 31, 2012
Series F Preferred Stock [Member]
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Dec. 31, 2012
Common Stock Withheld for Settlement of Employee Tax Liabilities [Member]
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Dec. 31, 2011
Common Stock Withheld for Settlement of Employee Tax Liabilities [Member]
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Dec. 31, 2010
Common Stock Withheld for Settlement of Employee Tax Liabilities [Member]
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| Stockholders 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 | |||||||||||||
| Number of preferred Stock issued to voting trust | 1 | |||||||||||||
| Number of Limited Vote Common Stock exchanged for common stock | (432,485) | (229,808) | 454,107 | 241,300 | ||||||||||
| Number of common stock shares received for each share of Common Stock converted | 1.05 | |||||||||||||
| Fraction of vote Common Stockholders were allowed on all matters other than election of the Board | 0.1 | |||||||||||||
| Treasury stock acquired | 8,133,329 | 8,133,329 | 370,007 | 299,804 | 243,821 | |||||||||
| Value of treasury stock acquired, cost method | $ 149,500,000 | $ 149,547,000 | $ 6,700,000 | $ 6,600,000 | $ 4,600,000 | |||||||||
| Aggregate authorized amount of common stock to be repurchased | 150,000,000 | |||||||||||||
| Reduction in net income as a result of non controlling interests | 16,027,000 | 11,901,000 | 2,381,000 | |||||||||||
| Carrying value of the investments held by Quanta in variable interest entities | 5,400,000 | 7,300,000 | ||||||||||||
| Distributions to noncontrolling interests | 17,970,000 | 5,954,000 | 2,395,000 | |||||||||||
| Carrying value of the investment held by noncontrolling interest in variable interest entities | $ 5,368,000 | $ 7,311,000 | ||||||||||||