Goodwill and Other Intangible Assets - Summary of Changes in Quanta's Goodwill (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2017	Jun. 30, 2017
Goodwill [Roll Forward]
Goodwill gross, beginning balance	$ 1,642,902
Accumulated impairment, beginning balance	(39,733)
Goodwill, beginning balance	1,603,169
Goodwill acquired	1,484	$ 19,200
Purchase price allocation adjustments	(1,278)
Foreign currency translation adjustments	12,942
Goodwill gross, ending balance	1,656,922	1,656,922
Accumulated impairment, ending balance	(40,605)	(40,605)
Goodwill, ending balance	1,616,317	1,616,317
Electric Power Infrastructure Services Division
Goodwill [Roll Forward]
Goodwill gross, beginning balance	1,253,979
Accumulated impairment, beginning balance	0
Goodwill, beginning balance	1,253,979
Goodwill acquired	1,484
Purchase price allocation adjustments	(619)
Foreign currency translation adjustments	7,892
Goodwill gross, ending balance	1,262,736	1,262,736
Accumulated impairment, ending balance	0	0
Goodwill, ending balance	1,262,736	1,262,736
Oil and Gas Infrastructure Services Division
Goodwill [Roll Forward]
Goodwill gross, beginning balance	388,923
Accumulated impairment, beginning balance	(39,733)
Goodwill, beginning balance	349,190
Goodwill acquired	0
Purchase price allocation adjustments	(659)
Foreign currency translation adjustments	5,050
Goodwill gross, ending balance	394,186	394,186
Accumulated impairment, ending balance	(40,605)	(40,605)
Goodwill, ending balance	$ 353,581	$ 353,581

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 foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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

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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.

+ References

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
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-Section 50
-Paragraph 1
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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