Segment Information (Segment Reporting By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Contract revenues	$ 170,586	$ 163,119
Operating income (loss)	(624)	(89)
Dredging Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	2,106	10,585
Environmental And Infrastructure Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(2,730)	(10,674)
Operating Segment [Member] | Dredging Segment [Member]
Segment Reporting Information [Line Items]
Contract revenues	153,054	145,013
Operating Segment [Member] | Environmental And Infrastructure Segment [Member]
Segment Reporting Information [Line Items]
Contract revenues	19,224	19,090
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Contract revenues	$ (1,692)	$ (984)