Property and Equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 304,204	$ 299,357
Less: accumulated depreciation	(195,843)	(191,407)
Net book value of depreciable assets	108,361	107,950
Property and equipment, net	147,683	146,278
Automobiles and trucks
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,802	1,940
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	42,555	38,062
Construction equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	156,695	166,203
Vessels and other equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	95,736	85,113
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,416	8,039
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	3,459	245
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 35,863	$ 38,083