Supplemental Balance Sheet Information - Uncompleted Contracts (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Supplemental Balance Sheet Data [Abstract]
Costs incurred on uncompleted contracts	$ 751,399	$ 741,590
Estimated earnings to date	138,998	165,862
Subtotal	890,397	907,452
Less – billings to date	(866,623)	(907,749)
Total	23,774	(297)
Costs and estimated earnings in excess of billings	75,371	62,401
Billings in excess of costs and estimated earnings	$ (51,597)	$ (62,698)

Liability attributable to (i) billings in excess of costs under the percentage of completion contract accounting method representing the difference between contractually invoiced amounts (billings) and revenue recognized based, for example, on costs incurred to estimated total costs at period end or (ii) contractually invoiced amounts (billings) in excess of costs incurred and accumulated under the completed contract accounting method that are expected to be realized within one year or one operating cycle, whichever is longer, from the reporting date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=68068069&loc=d3e57788-111642

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68068069&loc=d3e57807-111642

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68068069&loc=d3e57795-111642

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant