Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Sep. 30, 2014 USD ($)	Mar. 31, 2016 USD ($) item	Mar. 31, 2015 USD ($)	Jun. 26, 2014 USD ($) item
Commitments And Contingencies [Line Items]
Number of vessels owned with commitments | item		21
Deposit and interest collected			$ 4.2
Upon Notification of Bankruptcy
Commitments And Contingencies [Line Items]
Deposit reclassified to current receivable from construction in progress	$ 3.9
Interest income from accounts receivable	$ 0.3
U.S. Customs And Border Protection [Member]
Commitments And Contingencies [Line Items]
Number of affiliates that allegedly failed to properly report the importation of spare parts consumed by vessels | item				2
Amount of proposed duty				$ 1.4
Amount of proposed penalty on assessment				$ 5.7
Louisiana [Member] | Relocation of Corporate Headquarters to New Orleans [Member]
Commitments And Contingencies [Line Items]
Relocation incentive receivable		$ 10.3
Louisiana [Member] | Construction and Other Relocation Expenses [Member]
Commitments And Contingencies [Line Items]
Incentive received for offset costs related to construction of office building and other relocation expenses		$ 6.5