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Summary of Significant Accounting Policies (Revenue Recognition) - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) Project	Sep. 30, 2015 USD ($) Project	Sep. 30, 2016 USD ($) Project	Sep. 30, 2015 USD ($) Project	Dec. 31, 2015 USD ($)
Revenue Recognition [Line Items]
Revenues	$ 2,042,186,000	$ 1,939,438,000	$ 5,548,353,000	$ 5,673,164,000
Percent change in contract estimates impact on operating results is less than this percentage		5.00%	5.00%	5.00%
Increase in operating results due to change in contract estimates, percentage	6.30%
Change in contract estimates impact on operating results value gains identified that offset against losses disclosed				$ 11,500,000
Number of projects with significant losses | Project	1	2	1	2
Change orders and/or claims	$ 115,600,000		$ 115,600,000		$ 137,200,000
Alaska Power Plant Construction Project [Member]
Revenue Recognition [Line Items]
Losses on Contracts	3,000,000		54,800,000
Contract value of project	$ 201,000,000		$ 201,000,000
Project completion percentage	97.00%		97.00%
Power Plant Project in Alaska and Electric Transmission Project in Canada [Member]
Revenue Recognition [Line Items]
Losses on Contracts		$ 3,700,000		$ 45,000,000
Revenue Recognized For Losses Member | Alaska Power Plant Construction Project [Member]
Revenue Recognition [Line Items]
Revenues			$ 0

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Losses recognized in the current period on contracts which are expected to generate losses, which are probable and can be reasonably estimated, in a future period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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-Section S99
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