Revenue - Additional Information (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) contract
Revenue from Contract with Customer [Abstract]
Unbilled receivables, current	$ 9,336,000		$ 9,336,000		$ 7,894,000
Billings in excess of cost, current	344,000		344,000		$ 2,403,000
Revenue recognized, included in contract liability balance	$ 216,000	$ 741,000	$ 2,158,000	$ 1,560,000
Number of contracts identified as loss contracts \| contract	7		7		4
Provision for losses on contracts	$ 264,000		$ 264,000		$ 117,000
Remaining performance obligations	$ 14,417,000		$ 14,417,000		$ 12,652,000

Contract With Customer, Contracts In Progress, Number Of Contracts Identified As Loss Contracts

No definition available.

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130549-203045

+ Details

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- Definition

Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 35
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=68068069&loc=d3e57777-111642

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- References

No definition available.

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- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130556-203045

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- Definition

Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

+ References

No definition available.

+ Details

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