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Revenue From Contracts With Customers - Narrative (Details) $ in Thousands	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 ($)
Disaggregation of Revenue [Line Items]
Remaining performance obligation	$ 884,611		$ 884,611
Remaining performance obligation expected to be recognize the remainder of 2018	70.00%		70.00%
Minimum
Disaggregation of Revenue [Line Items]
Revenue recognition, contract term			12 months
Maximum
Disaggregation of Revenue [Line Items]
Revenue recognition, contract term			36 months
Transferred over Time | Product Concentration Risk | Revenue from Contract with Customer
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	83.00%	85.00%	84.00%	91.00%
Transferred at Point in Time | Product Concentration Risk | Revenue from Contract with Customer
Disaggregation of Revenue [Line Items]
Concentration risk, percentage	17.00%	15.00%	16.00%	9.00%
Heavy Civil Construction
Disaggregation of Revenue [Line Items]
Number of contracts (more than) | contract	150		150
Operating income (Loss)
Disaggregation of Revenue [Line Items]
Estimated construction gain (loss) before tax	$ 300	$ 1,800	$ 1,700	$ 1,100
Costs and Estimated Earnings in Excess of Billings
Disaggregation of Revenue [Line Items]
Unapproved change orders, amount	$ 8,700		$ 8,700
Contracts receivable unpaid project contract price					$ 10,000

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Amount of unpaid project contract price that the Company is entitled to.

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Revenue From Contract With Customer, Number Of Contracts

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- Definition

Represents the length of time the Company's contracts generally take to complete.

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Revenue, Remaining Performance Obligation, Percentage

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

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The amount of costs incurred on unapproved change orders when it is probable that the cost will be recovered through a change in the contract price.

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