Goodwill and Other Intangible Assets - Summary of Changes in Quanta's Goodwill (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill gross, beginning balance	$ 1,592,551
Accumulated impairment, beginning balance	(39,893)
Goodwill, beginning balance	1,552,658
Goodwill acquired	44,610	$ 51,935
Purchase price allocation adjustments	79
Foreign currency translation adjustments	14,891
Goodwill gross, ending balance	1,652,793	1,592,551
Accumulated impairment, ending balance	(40,555)	(39,893)
Goodwill, ending balance	1,612,238	1,552,658
Electric Power Division [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	1,226,245
Goodwill, beginning balance	1,226,245
Goodwill acquired	24,074
Purchase price allocation adjustments	293
Foreign currency translation adjustments	9,073
Goodwill gross, ending balance	1,259,685	1,226,245
Goodwill, ending balance	1,259,685	1,226,245
Oil and Gas Infrastructure Division [Member]
Goodwill [Line Items]
Goodwill gross, beginning balance	366,306
Accumulated impairment, beginning balance	(39,893)
Goodwill, beginning balance	326,413
Goodwill acquired	20,536
Purchase price allocation adjustments	(214)
Foreign currency translation adjustments	5,818
Goodwill gross, ending balance	393,108	366,306
Accumulated impairment, ending balance	(40,555)	(39,893)
Goodwill, ending balance	$ 352,553	$ 326,413

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=73531572&loc=d3e961-128460

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