Segment Information - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Contract revenues	$ 159,767	$ 137,420	$ 296,610	$ 276,177
Operating income (loss)	4,591	(2,466)	11,660	(3,948)
Depreciation and amortization expense			(14,211)	(15,119)
Total Assets	432,269		432,269		$ 433,285
Property and equipment, net	147,683		147,683		$ 146,278
Marine
Segment Reporting Information [Line Items]
Contract revenues	80,698		143,489
Concrete
Segment Reporting Information [Line Items]
Contract revenues	79,069		153,121
Intersegment Eliminations
Segment Reporting Information [Line Items]
Contract revenues			2,400
Operating Segments | Marine
Segment Reporting Information [Line Items]
Contract revenues	80,698	62,003	143,489	129,183
Operating income (loss)	3,642	(8,617)	9,907	(16,323)
Depreciation and amortization expense	(5,295)	(5,087)	(10,026)	(10,342)
Total Assets	268,642	252,348	268,642	252,348
Property and equipment, net	128,047	135,492	128,047	135,492
Operating Segments | Concrete
Segment Reporting Information [Line Items]
Contract revenues	79,069	75,417	153,121	146,994
Operating income (loss)	949	6,150	1,753	12,375
Depreciation and amortization expense	(2,136)	(2,505)	(4,185)	(4,777)
Total Assets	163,627	174,124	163,627	174,124
Property and equipment, net	$ 19,636	$ 16,009	$ 19,636	$ 16,009