Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment
Property, plant and equipment, gross	$ 262,476	$ 274,440
Less: accumulated depreciation	(190,091)	(186,615)
Property, plant and equipment net book value of depreciable assets	72,385	87,825
Property and equipment, net of depreciation	106,685	125,497
Automobiles and trucks
Property, Plant and Equipment
Property, plant and equipment, gross	2,354	2,379
Building and improvements
Property, Plant and Equipment
Property, plant and equipment, gross	34,797	44,324
Construction equipment
Property, Plant and Equipment
Property, plant and equipment, gross	137,134	142,661
Vessels and other equipment
Property, Plant and Equipment
Property, plant and equipment, gross	81,928	79,499
Office equipment
Property, Plant and Equipment
Property, plant and equipment, gross	6,263	5,577
Construction in progress
Property, Plant and Equipment
Property, plant and equipment, gross	6,415	1,809
Land
Property, Plant and Equipment
Property, plant and equipment, gross	$ 27,885	$ 35,863