Concentration of Risk and Enterprise Wide Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Concentration Risk [Line Items]
Contract revenues	$ 136,843	$ 138,757
Customer concentration risk \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 112,282		$ 124,142
Concentration risk, percentage	100.00%		100.00%
Customer concentration risk \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%
Contract revenues	$ 136,843	$ 138,757
Customer concentration risk \| Federal Government \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 4,137		$ 3,509
Concentration risk, percentage	4.00%		3.00%
Customer concentration risk \| Federal Government \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%	14.00%
Contract revenues	$ 13,023	$ 19,731
Customer concentration risk \| State Governments \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 6,745		$ 4,503
Concentration risk, percentage	6.00%		3.00%
Customer concentration risk \| State Governments \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	6.00%	9.00%
Contract revenues	$ 8,376	$ 12,019
Customer concentration risk \| Local Governments \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 17,593		$ 18,256
Concentration risk, percentage	16.00%		15.00%
Customer concentration risk \| Local Governments \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	17.00%	17.00%
Contract revenues	$ 23,230	$ 23,827
Customer concentration risk \| Private Companies \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 83,807		$ 97,874
Concentration risk, percentage	74.00%		79.00%
Customer concentration risk \| Private Companies \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	67.00%	60.00%
Contract revenues	$ 92,214	$ 83,180

Trade Accounts Receivable and Contract Receivable Retainage, Net

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=84177426&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13537-108611

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- Definition

Amount of revenue earned from products sold or services provided under the terms of a contract, including, but not limited to, government contracts and construction contracts, classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

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