Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 299,357	$ 300,601
Less: accumulated depreciation	(191,407)	(181,293)
Property, Pant and Equipment, Net Book Value of Depreciable Assets	107,950	119,308
Property and equipment, net	146,278	158,082
Automobiles and trucks
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,940	2,525
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	38,062	37,269
Construction equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	166,203	165,023
Dredges and dredging equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	85,113	88,659
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,039	7,125
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	245	543
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 38,083	$ 38,231