Quanta Services, Inc. Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Partial withdrawal liability	$ 32.6	$ 32.6
Multiemployer defined contribution plan contributions	87.0	46.7	35.8
Four Zero One K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of contribution by employer of each employee's contribution up to 3%	100.00%
Percentage of contribution by employer of each employee who contributes between three and six percent	50.00%
Percentage of employee contribution, lower range	3.00%
Percentage of employee contribution, high range	6.00%
Contributions to all non union defined contribution plans	$ 11.0	$ 9.5	$ 8.9
Red Zone [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage Funded in this Zone	Less than 65%
Yellow Zone [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage Funded in this Zone	Less than 80%
Green Zone [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage Funded in this Zone	at least 80%