Segment Information - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Contract revenues	$ 165,985	$ 159,767	$ 309,090	$ 296,610
Operating income (loss)	(423)	4,591	(6,600)	11,660
Depreciation and amortization expense			(13,108)	(14,211)
Total assets	362,789		362,789		$ 312,870
Property and equipment, net of depreciation	135,045		135,045		$ 148,003
Marine
Segment Reporting Information [Line Items]
Contract revenues	89,023	80,698	150,510	143,489
Concrete
Segment Reporting Information [Line Items]
Contract revenues	76,962	79,069	158,580	153,121
Intersegment Eliminations
Segment Reporting Information [Line Items]
Contract revenues	200	100	2,400	2,400
Operating Segments | Marine
Segment Reporting Information [Line Items]
Contract revenues	89,023	80,698	150,510	143,489
Operating income (loss)	9	3,642	(6,447)	9,907
Depreciation and amortization expense	(5,069)	(5,295)	(10,015)	(10,026)
Total assets	236,917	268,642	236,917	268,642
Property and equipment, net of depreciation	117,262	128,047	117,262	128,047
Operating Segments | Concrete
Segment Reporting Information [Line Items]
Contract revenues	76,962	79,069	158,580	153,121
Operating income (loss)	(432)	949	(153)	1,753
Depreciation and amortization expense	(2,153)	(2,136)	(4,247)	(4,185)
Total assets	125,872	163,627	125,872	163,627
Property and equipment, net of depreciation	$ 17,783	$ 19,636	$ 17,783	$ 19,636