Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 295,262	$ 299,357
Less: accumulated depreciation	(192,480)	(191,407)
Net book value of depreciable assets	102,782	107,950
Property and equipment, net	144,868	146,278
Automobiles and trucks
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,863	1,940
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	38,053	38,062
Construction equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	153,309	166,203
Vessels and other equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	94,945	85,113
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,092	8,039
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,003	245
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 38,083	$ 38,083