Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Benefit Plans [Line Items]
Multiemployer defined contribution and other benefit plan contributions other than MEP DBP	$ 139.3	$ 147.1	$ 129.0
Contributions to the deferred compensation plans	1.0	1.0	0.3
Deferred compensation obligations included in other long-term liabilities	19.1	11.7
Deferred compensation obligations included in other long-term assets	$ 17.9	11.3
401K Plan [Member]
Employee Benefit Plans [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 Quanta 401(k) Plan	$ 21.9	$ 17.7	$ 13.9
Red Zone [Member]
Employee Benefit Plans [Line Items]
Percentage Funded in this Zone	Less than 65 %
Yellow Zone [Member]
Employee Benefit Plans [Line Items]
Percentage Funded in this Zone	Less than 80 %
Green Zone [Member]
Employee Benefit Plans [Line Items]
Percentage Funded in this Zone	at least 80 %