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Employee Benefit Plans - Narrative (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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 | $ 110,082 | $ 85,235 | $ 77,015
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 | $ 26,300 | 21,900 | 17,700
Contributions to the deferred compensation plans | 1,100 | 1,000 | 1,000
Deferred compensation obligations included in other long-term liabilities | 30,100 | 19,100 |
Investments in company-owned life insurance policies | $ 28,700 | 17,900 |
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% |  |
Union Employees |  |  |
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 | $ 171,400 | $ 139,300 | $ 147,100

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- Definition Defined Contribution Plan, Employer Matching Contribution, Percent of Match By Employer Up To Specific Percentage + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of assets held under deferred compensation agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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