Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 305,024	$ 299,357
Less: accumulated depreciation	(199,198)	(191,407)
Net book value of depreciable assets	105,826	107,950
Property and equipment, net	144,387	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	43,247	38,062
Construction equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	156,611	166,203
Vessels and other equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	95,525	85,113
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,839	8,039
Construction -in- progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,698	245
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 35,863	$ 38,083