Segment Information - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($) segment	Sep. 30, 2019 USD ($) segment	Sep. 30, 2018 USD ($) segment	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2	2	2	2
Contract revenues	$ 199,507	$ 125,073	$ 508,597	$ 421,682
Operating income (loss)	6,092	(7,405)	(508)	4,254
Depreciation and amortization expense			(19,609)	(21,134)
Total assets	377,107		377,107		$ 312,870
Property and equipment, net of depreciation	134,056		134,056		$ 148,003
Marine
Segment Reporting Information [Line Items]
Contract revenues	107,404	63,479	257,914	206,967
Concrete
Segment Reporting Information [Line Items]
Contract revenues	92,103	61,594	250,683	214,715
Intersegment Eliminations
Segment Reporting Information [Line Items]
Contract revenues	300		500	2,400
Operating Segments | Marine
Segment Reporting Information [Line Items]
Contract revenues	107,404	63,479	257,914	206,967
Operating income (loss)	4,863	(5,559)	(1,584)	4,348
Depreciation and amortization expense	(4,960)	(4,746)	(14,975)	(14,772)
Total assets	252,995	269,501	252,995	269,501
Property and equipment, net of depreciation	117,071	125,231	117,071	125,231
Operating Segments | Concrete
Segment Reporting Information [Line Items]
Contract revenues	92,103	61,594	250,683	214,715
Operating income (loss)	1,229	(1,846)	1,076	(94)
Depreciation and amortization expense	(2,120)	(2,176)	(6,367)	(6,362)
Total assets	124,112	155,247	124,112	155,247
Property and equipment, net of depreciation	$ 16,985	$ 19,156	$ 16,985	$ 19,156