Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 304,728	$ 299,357
Less: accumulated depreciation	(195,373)	(191,407)
Property, Pant and Equipment, Net Book Value of Depreciable Assets	109,355	107,950
Property and equipment, net	148,003	146,278
Automobiles and trucks
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,709	1,940
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	43,628	38,062
Construction equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	161,113	166,203
Dredges and dredging equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	90,217	85,113
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,061	8,039
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,785	245
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 35,863	$ 38,083