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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements payable within one year (or the operating cycle, if longer).

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- Definition

Aggregate cash paid by the entity during the period to settle equity instruments granted under equity-based payment arrangements.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Equity-Based Compensation - RSUs to be Settled in Cash (Detail) - Restricted Stock Units to be Settled in Cash - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount in cash received for each RSU is equal to the fair value of this number of Quanta common stock shares (in shares)			1
Compensation expense related to RSUs to be settled in cash	$ 1.2	$ 2.3	$ 4.0	$ 6.2
Payments to settle liabilities under compensation plan	0.1	$ 1.4	6.1	$ 7.5
Accrued liabilities under compensation plan	$ 2.5		$ 2.5		$ 4.6
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for RSUs to be settled in cash			2 years
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for RSUs to be settled in cash			3 years