Debt Obligations - Additional Information (Detail) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Oct. 30, 2013
Line of Credit Facility [Line Items]
Letters of credit and bank guarantees under the credit facility	$ 336,700,000
Amount borrowed under the credit facility	68,793,000
Credit facility available for revolving loans or issuing new letters of credit	919,500,000
U S Dollar [Member]
Line of Credit Facility [Line Items]
Letters of credit and bank guarantees under the credit facility	225,100,000
Canadian Dollars [Member]
Line of Credit Facility [Line Items]
Amount borrowed under the credit facility	68,793,000
Canada and Australia Dollar [Member]
Line of Credit Facility [Line Items]
Letters of credit and bank guarantees under the credit facility	111,600,000
Second Amendment [Member]
Line of Credit Facility [Line Items]
Reduction in Quanta's maximum funded debt and maximum senior debt by all cash and cash equivalents in excess of amount	25,000,000
Percentage of capital stock of direct foreign subsidiaries required to secure credit agreement	65.00%
Amount of availability under the credit agreement and/or cash and cash equivalents on hand that must be present to allow for cash payments of dividends and stock repurchases	100,000,000
Cross default provisions with debt instruments exceeding this amount	75,000,000
First Amendment [Member]
Line of Credit Facility [Line Items]
Senior secured revolving credit facility		700,000,000
Reduction in Quanta's maximum funded debt and maximum senior debt by all cash and cash equivalents in excess of amount		25,000,000
Prior and After April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Senior secured revolving credit facility	1,325,000,000
Maturity date of senior secured revolving credit facility	Oct. 30, 2018
Option to increase revolving commitments under the credit agreement	300,000,000
Prior to April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Commitment fee	0.20%
Minimum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Commitment fee		0.20%
Minimum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Commitment fee	0.20%
Maximum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Commitment fee		0.45%
Maximum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Commitment fee	0.40%
Standby Letters of Credit [Member] | Prior to April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.25%
Standby Letters of Credit [Member] | Minimum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		1.25%
Standby Letters of Credit [Member] | Minimum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.125%
Standby Letters of Credit [Member] | Maximum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		2.50%
Standby Letters of Credit [Member] | Maximum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	2.125%
Performance Letters of Credit [Member] | Prior to April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	0.75%
Performance Letters of Credit [Member] | Minimum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	0.675%
Performance Letters of Credit [Member] | Maximum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.275%
Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only [Member] | Prior to April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.25%
Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only [Member] | Minimum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		1.25%
Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only [Member] | Minimum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.125%
Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only [Member] | Maximum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		2.50%
Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only [Member] | Maximum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	2.125%
Excess of Base Rate Domestic Borrowings Only [Member] | Prior to April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	0.25%
Excess of Base Rate Domestic Borrowings Only [Member] | Minimum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		0.25%
Excess of Base Rate Domestic Borrowings Only [Member] | Minimum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	0.125%
Excess of Base Rate Domestic Borrowings Only [Member] | Maximum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		1.50%
Excess of Base Rate Domestic Borrowings Only [Member] | Maximum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.125%
Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings [Member] | Prior to April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.25%
Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings [Member] | Minimum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		1.25%
Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings [Member] | Minimum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.125%
Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings [Member] | Maximum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		2.50%
Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings [Member] | Maximum [Member] | Effective April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	2.125%
Excess of Federal Funds Rate [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	0.50%
Excess of Federal Funds Rate [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		0.50%
Excess of Euro Currency Rate [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate	1.00%
Excess of Euro Currency Rate [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		1.00%
Swing Line Loans [Member] | Prior and After April 1, 2014 [Member] | Second Amendment [Member] | U S Dollar [Member]
Line of Credit Facility [Line Items]
Senior secured revolving credit facility	50,000,000
Swing Line Loans [Member] | Prior and After April 1, 2014 [Member] | Second Amendment [Member] | Canadian Dollars [Member]
Line of Credit Facility [Line Items]
Senior secured revolving credit facility	30,000,000
Swing Line Loans [Member] | Prior and After April 1, 2014 [Member] | Second Amendment [Member] | Australian Dollars [Member]
Line of Credit Facility [Line Items]
Senior secured revolving credit facility	20,000,000
Revolving Loans and Letter of Credit in Alternative Currencies [Member] | Prior and After April 1, 2014 [Member] | Second Amendment [Member]
Line of Credit Facility [Line Items]
Senior secured revolving credit facility	$ 400,000,000
Performance Letters of Credit [Member] | Minimum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		0.75%
Performance Letters of Credit [Member] | Maximum [Member] | First Amendment [Member]
Line of Credit Facility [Line Items]
Debt Instrument Basis Spread On Variable Rate		1.50%