Employee Benefit Plans - Summary of Plan Information Relating to Participation in Multi-Employer Pension Plans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Multiemployer Plans [Line Items]
Contributions	$ 63,572	$ 45,202	$ 40,705
National Electrical Benefit Fund [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	53-0181657-001
PPA Zone Status	Green	Green
Subject to Financial Improvement/ Rehabilitation Plan	No
Contributions	18,509	9,704	8,174
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	Varies through November 2015
Pipeline Industry Pension Fund [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	73-6146433-001
PPA Zone Status	Green	Green
Subject to Financial Improvement/ Rehabilitation Plan	No
Contributions	7,434	101	60
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	December 2012
Central Pension Fund of the IUOE & Participating Employers [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	36-6052390-001
PPA Zone Status	Green	Green
Subject to Financial Improvement/ Rehabilitation Plan	No
Contributions	6,843	4,439	10,446
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	Varies through January 2013
Eighth District Electrical Pension Fund [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	84-6100393-001
PPA Zone Status	Green	Green
Subject to Financial Improvement/ Rehabilitation Plan	No
Contributions	4,415	3,533	1,917
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	Varies through May 2015
Plan years in which Quanta contributions were five percent or more of total plan contributions	2011 and 2010
Laborers National Pension Fund [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	75-1280827-001
PPA Zone Status	Green	Green
Subject to Financial Improvement/ Rehabilitation Plan	No
Contributions	1,906	1,903	4,329
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	April 2013
Plan years in which Quanta contributions were five percent or more of total plan contributions	2010
NECA-IBEW Pension Trust [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	51-6029903-001
PPA Zone Status	Green	Green
Subject to Financial Improvement/ Rehabilitation Plan	No
Contributions	19	6,707	5,928
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	Varies through June 2014
Plan years in which Quanta contributions were five percent or more of total plan contributions	2011 and 2010
Joint Pension Local Union 164 IBEW [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	22-6031199-001
PPA Zone Status	Yellow	Yellow
Subject to Financial Improvement/ Rehabilitation Plan	Implemented
Contributions	515	2,887	39
Surcharge Imposed	No
Expiration Date of Collective Bargaining Agreement	May 2014
Plan years in which Quanta contributions were five percent or more of total plan contributions	2011
IBEW Local 246 Pension Plan [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	34-6582842-001
PPA Zone Status	Red	Red
Subject to Financial Improvement/ Rehabilitation Plan	Implemented
Contributions	130	1,977	61
Surcharge Imposed	Yes
Expiration Date of Collective Bargaining Agreement	October 2012
Plan years in which Quanta contributions were five percent or more of total plan contributions	2011
Central States, Southeast, and Southwest Areas Pension Plan [Member]
Multiemployer Plans [Line Items]
Employer Identification Number	36-6044243-001
PPA Zone Status	Red	Red
Subject to Financial Improvement/ Rehabilitation Plan	Implemented
Contributions	22	540	2,100
Surcharge Imposed	Yes
Expiration Date of Collective Bargaining Agreement	Varies through April 2014
All Other Plans [Member]
Multiemployer Plans [Line Items]
Contributions	$ 23,779	$ 13,411	$ 7,651

Multiemployer Plans Number

No definition available.

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- Definition

Significant Periods Of Multiemployer Contributions Exceeding Specified Percentage

+ References

No definition available.

+ Details

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- Definition

Amount of contributions made to multiemployer plans by the employer. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450702-114947

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 9

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450691-114947

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 5

-Subparagraph (e)(1)

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Indicate the multiemployer plan's certified zone status as currently required by the Pension Protection Act of 2006 or a subsequent amendment thereof. The zone status categories are red (critical status), orange (seriously endangered), yellow (endangered), and green (none of the above). The acceptable values are "red", "orange", "yellow", "green", "other", and "NA". A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 5

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Description of the significant collective-bargaining arrangements within the range of expiration dates for collective-bargaining arrangements requiring contributions to a multiemployer plan as well as other information to help investors understand the significance of the collective-bargaining agreements and when they expire. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 5

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Indicate whether a funding improvement plan or rehabilitation plan has been implemented or is pending for a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "pending", "implemented", "other", and "NA".

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 5

-Subparagraph (f)(1)

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947

+ Details

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- Details

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- Definition

Indicate whether the employer paid a surcharge to the pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. The acceptable values are "no", "yes", and "NA".

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 5

-Subparagraph (f)(2)

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450657-114947

+ Details

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Balance Type:	na
Period Type:	duration