Employee Benefit Plans - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percent of employees covered by collective bargaining agreements	35.00%
Multiemployer defined contribution and other benefit plan contributions other than MEP DBP	$ 134,197	$ 126,191	$ 110,082
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 3% and 6%	50.00%
Contributions to Quanta 401(k) Plan	$ 41,400	33,400	26,300
Contributions to the deferred compensation plans	1,100	1,100	1,100
Deferred compensation obligations included in other long-term liabilities	47,300	33,400
Investments in company-owned life insurance policies	$ 45,800	33,500
Minimum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of employee contribution, lower range	3.00%
Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of employee contribution, lower range	6.00%
Multiemployer Defined Contribution and Other Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Multiemployer defined contribution and other benefit plan contributions other than MEP DBP	$ 201,300	$ 174,700	$ 171,400

Defined Contribution Plan, Employer Matching Contribution, Percent of Match By Employer Up To Specific Percentage

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Defined Contribution Plan, Employer Matching Contribution, Percent of Match By Employer Of Each Employee Who Contributes To Plan

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Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

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Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable beyond one year (or the operating cycle, if longer).

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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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Amount of cost for defined contribution plan.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI).

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Amount of contributions made to multiemployer plan by employer.

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Percentage of employee participants subject to a collective bargaining arrangement to all participants in 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.

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