Debt Obligations - Additional Information (Detail) (USD $)	12 Months Ended			12 Months Ended	9 Months Ended	12 Months Ended			12 Months Ended				12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010	May 14, 2010	Dec. 31, 2010 3.75% Convertible Subordinated Notes [Member]	Sep. 30, 2011 Prior Credit Facility [Member]	Dec. 31, 2011 Prior Credit Facility [Member]	Aug. 02, 2011 Prior Credit Facility [Member]	Dec. 31, 2012 Revolving Loans and Letter of Credit in Alternative Currencies [Member]	Dec. 31, 2012 Minimum [Member]	Dec. 31, 2011 Minimum [Member]	May 14, 2010 Minimum [Member] 3.75% Convertible Subordinated Notes [Member]	Dec. 31, 2012 Minimum [Member] Performance Letter Of Credit [Member]	Dec. 31, 2011 Minimum [Member] Prior Credit Facility [Member]	Dec. 31, 2012 Maximum [Member]	Dec. 31, 2011 Maximum [Member]	Dec. 31, 2012 Maximum [Member] Performance Letter Of Credit [Member]	Dec. 31, 2011 Maximum [Member] Prior Credit Facility [Member]
Line Of Credit Facility Covenant Compliance [Line Items]
Senior secured revolving credit facility	$ 700,000,000						$ 475,000,000	$ 100,000,000
Maturity date of senior secured revolving credit facility	Aug. 02, 2016				Sep. 19, 2012
Letters of credit issued under the credit facility	183,200,000
Amount borrowed under the credit facility	0
Credit facility available for revolving loans or issuing new letters of credit	516,800,000
Interest rate in excess of Eurocurrency rate applicable to domestic borrowings only, plus Mandatory Cost									1.25%					2.50%
Interest rate in excess of Base Rate, domestic borrowings only									0.25%					1.50%
Interest rate of credit agreement for foreign borrowings, plus mandatory costs									1.25%					2.50%
Letter of credit fee									1.25%			0.75%	0.875%	2.50%		1.50%	1.75%
Commitment fee									0.20%				0.15%	0.45%			0.35%
Reduction in Quanta's maximum funded debt and maximum senior debt by all cash and cash equivalents in excess of amount	25,000,000
Base rate in excess of Federal Funds Rate	0.50%					0.50%
One possible rate is this rate in excess of the Eurocurrency Rate	1.00%
Percentage of capital stock of direct foreign subsidiaries required to secure credit agreement	65.00%
Cross default provisions with debt instruments exceeding this amount	30,000,000
Interest rate in excess of Base Rate													0.00%				0.75%
Interest rate in excess of Eurodollar Rate													0.875%				1.75%
Debt Instrument, Face Amount			143,800,000
Redemption price as a percentage of the principle amount of the 3.75% convertible subordinated notes			101.607%
Payment of aggregate Redemption Price		146,100,000
Loss on early extinguishment of debt, net		(7,107,000)		(7,100,000)
Non cash gain (loss) included in loss on extinguishment of debt				(3,500,000)
Redemption premium on convertible subordinated notes				2,300,000
Non-cash gain (loss) from the write-off of financing costs				$ (1,300,000)
Redemption premium for payment of aggregate redemption price				1.607%
Annual interest rate									0.00%	0.00%	3.75%			8.00%	8.00%