Goodwill and Other Intangible Assets - Summary of Changes in Quanta's Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Mar. 31, 2018
Goodwill [Roll Forward]
Goodwill gross, beginning balance	$ 1,966,432
Accumulated impairment, beginning balance	(97,832)
Goodwill, beginning balance	1,868,600
Goodwill acquired	41,709	$ 344,100
Foreign currency translation adjustments	(7,438)
Goodwill gross, ending balance	2,000,474	2,000,474
Accumulated impairment, ending balance	(97,603)	(97,603)
Goodwill, ending balance	1,902,871	1,902,871
Electric Power Infrastructure Services Division
Goodwill [Roll Forward]
Goodwill gross, beginning balance	1,272,527
Accumulated impairment, beginning balance	0
Goodwill, beginning balance	1,272,527
Goodwill acquired	41,709
Foreign currency translation adjustments	(4,699)
Goodwill gross, ending balance	1,309,537	1,309,537
Accumulated impairment, ending balance	0	0
Goodwill, ending balance	1,309,537	1,309,537
Oil and Gas Infrastructure Services Division
Goodwill [Roll Forward]
Goodwill gross, beginning balance	693,905
Accumulated impairment, beginning balance	(97,832)
Goodwill, beginning balance	596,073
Goodwill acquired	0
Foreign currency translation adjustments	(2,739)
Goodwill gross, ending balance	690,937	690,937
Accumulated impairment, ending balance	(97,603)	(97,603)
Goodwill, ending balance	$ 593,334	$ 593,334

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=77989000&loc=SL49117168-202975

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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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 before 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.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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