Leases (Narrative) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015 USD ($) agreement item	Dec. 31, 2014 USD ($)	Dec. 31, 2012 USD ($) agreement
Leases [Line Items]
Number of vessels under bareboat charter or lease agreements | item		7
Number of sale/ leaseback transactions | agreement				3
Number of lease agreements impose certain financial covenants | agreement		3
Vessel repurchased, amount			$ 55,600
Unamortized deferred gain recorded as reduction in cost basis of purchased asset			11,200
Depreciation expense		$ 23,002	26,984
Rent expense		1,000	$ 21,100
If Defaulted on any of Operating Lease Agreements [Member]
Leases [Line Items]
Stipulated loss value if forced to buy back vessels		$ 73,500
Relocation of Corporate Headquarters to New Orleans [Member]
Leases [Line Items]
Number of incentives from the State of Louisiana | item		2
Louisiana [Member] | Relocation of Corporate Headquarters to New Orleans [Member]
Leases [Line Items]
Incentive received		$ 10,300
Louisiana [Member] | New Orleans Office Building [Member]
Leases [Line Items]
Incentive received		5,200
Louisiana [Member] | Other Relocation Expenses [Member]
Leases [Line Items]
Incentive received		5,100
Mobile, Alabama Corporate Office Lease [Member]
Leases [Line Items]
Commitment to pay early cancelation of lease		2,700
New Orleans Office Building [Member] | Louisiana [Member]
Leases [Line Items]
Office space lease agreement term	18 months
Leasehold Improvements [Member] | Mobile, Alabama Corporate Office Lease [Member]
Leases [Line Items]
Depreciation expense		$ 900
Container Vessels [Member] | Jones Act [Member]
Leases [Line Items]
Number of vessels under operating contracts | item		2
Multi-purpose vessels [Member] | Jones Act [Member]
Leases [Line Items]
Number of vessels under operating contracts | item		2
Pure Car Truck Carriers [Member] | Specialty Contracts [Member]
Leases [Line Items]
Number of vessels under bareboat charter or lease agreements | item		2
1998-built PCTC [Member]
Leases [Line Items]
Lease term				6 years
Gain on sale-leaseback				$ 11,700
Sale leaseback deferred gain net		$ 5,700
Deferred gain recognized each year over the term of the lease				$ 1,900
1999-built PCTC [Member]
Leases [Line Items]
Lease term				6 years
Molten Sulphur Carrier [Member]
Leases [Line Items]
Lease term				7 years
Gain on sale-leaseback				$ 8,000
Sale leaseback deferred gain net		$ 4,600
Deferred gain recognized each year over the term of the lease				$ 1,200
Multi-Purpose Heavy Lift Vessel [Member] | Specialty Contracts [Member]
Leases [Line Items]
Number of vessels under bareboat charter or lease agreements | item		2
Tankers [Member] | Specialty Contracts [Member]
Leases [Line Items]
Number of vessels under bareboat charter or lease agreements | item		2