Segment Information (Segment Reporting By Segment) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment Reporting Information [Line Items]
Contract revenues	$ 163,119	$ 174,557
Operating income (loss)	(89)	(7,258)
Dredging Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	10,585	7,874
Environmental And Infrastructure Segment [Member]
Segment Reporting Information [Line Items]
Operating income (loss)	(10,674)	(15,132)
Operating Segment [Member] | Dredging Segment [Member]
Segment Reporting Information [Line Items]
Contract revenues	145,013	154,128
Operating Segment [Member] | Environmental And Infrastructure Segment [Member]
Segment Reporting Information [Line Items]
Contract revenues	19,090	21,552
Intersegment Revenues [Member]
Segment Reporting Information [Line Items]
Contract revenues	$ (984)	$ (1,123)