Concentration of Risk and Enterprise Wide Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Concentration Risk [Line Items]
Contract revenues	$ 143,105	$ 136,843
Customer concentration risk \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 118,864		$ 108,375
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	$ 143,105	$ 136,843
Customer concentration risk \| Federal Government \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 3,533		$ 2,319
Concentration risk, percentage	3.00%		2.00%
Customer concentration risk \| Federal Government \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	7.00%	10.00%
Contract revenues	$ 10,277	$ 13,023
Customer concentration risk \| State Governments \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 509		$ 916
Concentration risk, percentage	0.00%		1.00%
Customer concentration risk \| State Governments \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	3.00%	6.00%
Contract revenues	$ 4,055	$ 8,376
Customer concentration risk \| Local Governments \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 39,053		$ 30,187
Concentration risk, percentage	33.00%		28.00%
Customer concentration risk \| Local Governments \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	31.00%	17.00%
Contract revenues	$ 44,430	$ 23,230
Customer concentration risk \| Private Companies \| Trade and contract retainage receivables
Concentration Risk [Line Items]
Trade and retainage receivables	$ 75,769		$ 74,953
Concentration risk, percentage	64.00%		69.00%
Customer concentration risk \| Private Companies \| Contract revenues
Concentration Risk [Line Items]
Concentration risk, percentage	59.00%	67.00%
Contract revenues	$ 84,343	$ 92,214

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.

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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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