Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 291,197	$ 304,728
Less: accumulated depreciation	(194,225)	(195,373)
Net book value of depreciable assets	96,972	109,355
Property and equipment, net of depreciation	136,841	148,003
Automobiles and trucks
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,668	1,709
Building and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	43,628	43,628
Construction equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	156,015	161,113
Vessels and other equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	81,772	90,217
Office equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	8,114	8,061
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,006	2,785
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 35,863	$ 35,863