Equipment Acquisitions, Dispositions and Depreciation and Impairment Policies (Useful Life) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended	6 Months Ended	9 Months Ended
	Jul. 02, 2011 Y	Jun. 30, 2011 Y	Sep. 30, 2012 Y
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			25
Increase In Operating Income From Change In Estimate			8.4
Increase In Net Income From Change In Estimate			5.4
Increase In Diluted Earnings Per Share From Change In Estimate			0.26
Offshore Support Vessels [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			20
Wind Farm Utility Vessel [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			10
Helicopters [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)	15	12	15	[1]
Property, Plant and Equipment, Salvage Value, Percentage	40.00%	30.00%
Inland River Dry Cargo And Deck Barges [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			20
Inland River Liquid Tank Barges [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			25
Inland River Towboats [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			25
U S Flag Tankers [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			25
R O R O Vessels [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			20
Harbor And Offshore Tugs [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life (in years)			25

[1] Effective July 1, 2011, the Company changed its estimated useful life and salvage value for helicopters from 12 to 15 years and 30% to 40%, respectively, due to improvements in new helicopter models that continue to increase their long-term value and make them viable for operation over a longer period of time. For the nine months ended September 30, 2012, the change in estimate increased operating income by $8.4 million, net income by $5.4 million, and basic and diluted earnings per share by $0.26.