Equipment Acquisitions, Dispositions and Depreciation and Impairment Policies (Narrative) (Details) (USD $)	3 Months Ended	6 Months Ended			12 Months Ended				6 Months Ended		12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Offshore Support Vessels Specialty [Member] equipment	Dec. 31, 2012 Offshore Support Vessels Specialty [Member] equipment	Dec. 31, 2012 Offshore Support Vessels Crew [Member] equipment	Dec. 31, 2012 Offshore Support Vessels Mini Supply [Member] equipment	Dec. 31, 2012 Offshore Support Vessels Supply [Member] equipment	Jun. 30, 2013 Liftboats [Member] equipment	Jun. 30, 2013 Wind Farm Utility Vessel [Member] equipment	Dec. 31, 2012 Inland River Dry Cargo And Deck Barges [Member] equipment	Jun. 30, 2013 Inland River Liquid Tank Barges [Member] equipment	Dec. 31, 2012 Inland River Liquid Tank Barges [Member] equipment	Jun. 30, 2013 U.S.-flag Harbor Tugs [Member]	Dec. 31, 2012 U.S.-flag Harbor Tugs [Member] equipment	Jun. 30, 2013 Mexmar [Member]	Jun. 30, 2013 Gains on Asset Dispositions and Impariments, Net [Member]	Dec. 31, 2012 Gains on Asset Dispositions and Impariments, Net [Member]
Property, Plant and Equipment [Line Items]
Payments to Acquire Property, Plant, and Equipment		$ 87,931,000	$ 99,507,000
Number Of Equipments Delivered				1					2	2		2			3
Number Of Equipments Sold					1	2	1	1	3		16		8		2
Sales Price Of Equipment		132,400,000
Proceeds from Sale of Property, Plant and Equipment, Excluding Deposits on Future Equipment Sales		125,100,000
Vendor Credits		200,000
Proceeds from disposition of property and equipment		125,432,000	7,394,000													60,500,000
Proceeds from Issuance of Secured Debt		7,100,000
Gains (Losses) on Sales of Assets	15,200,000																	12,900,000
Deferred Gains on Asset Sales		2,300,000
Amortization Of Deferred Gains Included In Gains On Asset Dispositions And Impairments, Net		(1,431,000)	(2,039,000)														1,400,000
Proceeds from Other Deposits		300,000
Asset Impairment Charges														$ 3,000,000