Basis Of Presentation and Significant Accounting Policies (Details)	3 Months Ended
	Mar. 31, 2018
Minimum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life	20 years
Vessels | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Vessels | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	30 years
Building | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	10 years
Building | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	50 years
Machinery and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Machinery and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	20 years
Software | Minimum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life	3 years
Software | Maximum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life	10 years
Internet website costs | Maximum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life	3 years