Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 379,475	$ 364,357
Less: Accumulated depreciation and amortization	(231,391)	(209,466)
Property, Plant and Equipment, Net	148,084	154,891
Land [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 7,733	5,468
Estimated Useful Life	0 years
Building and Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 22,718	21,660
Building and Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	39 years
Building and Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Construction Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 340,060	329,299
Construction Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	12 years
Construction Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 8,964	$ 7,930
Office Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	10 years
Office Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years