Debt And Lease Obligations (Narrative) (Details)		1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 06, 2016 USD ($)	Apr. 30, 2015 USD ($)	Mar. 31, 2016 USD ($) item agreement	Mar. 31, 2015 USD ($) item	Dec. 31, 2015 USD ($) loan item	Dec. 31, 2013
Line of Credit Facility [Line Items]
Number of secured financing agreements | agreement			5
Current maturities of long-term debt, net			$ 113,721,000		$ 156,807,000
Debt issuance costs			3,300,000		3,000,000
Amortization of debt issuance costs			400,000	$ 200,000
Long term debt carrying amount			$ 117,070,000		159,844,000
Related debt paid off				13,500,000
Loss on Extinguishment of Debt				(95,000)
Number of vessels under bareboat charter or lease agreements | item			7
Number of vessels under operating lease contracts with certain financial covenants | item			3
Unamortized deferred gains related to leased vessels			$ 22,500,000		15,300,000
Deferred gains on sale of property			21,347,000		14,944,000
Amortization expense slightly offset deferred gains			855,000	948,000
Deferred debt issuance costs reclassified from deferred charges, net			3,349,000		3,037,000
Total amount paid off				2,500,000
Mobile, Alabama Corporate Office Lease [Member]
Line of Credit Facility [Line Items]
Commitment to pay early cancelation of lease			2,700,000
Tampa, Florida [Member]
Line of Credit Facility [Line Items]
Lease agreement for office space						5 years
Lease term of office space						60 months
Other Long-term Liabilities [Member]
Line of Credit Facility [Line Items]
Unamortized deferred gains related to leased vessels			21,300,000		14,900,000
Accounts Payable And Accrued Expenses [Member]
Line of Credit Facility [Line Items]
Unamortized deferred gains related to leased vessels			1,200,000		$ 400,000
If Defaulted on any of Operating Lease Agreements [Member]
Line of Credit Facility [Line Items]
Stipulated loss value if forced to buy back vessels			$ 70,600,000
Number of vessels to be purchased back | item			3
Partially Offset Costs Related To New Orleans Office Building [Member] | Louisiana [Member]
Line of Credit Facility [Line Items]
Grant as incentive for relocation			$ 5,200,000
Other Relocation Expenses [Member] | Louisiana [Member]
Line of Credit Facility [Line Items]
Grant as incentive for relocation			$ 5,100,000
DVB Bank SE [Member]
Line of Credit Facility [Line Items]
Debt instrument effective interest rate percentage		4.16%
Amortization period		10 years
Final quarterly balloon payment		$ 16,800,000
Loss on Extinguishment of Debt		$ 300,000
Regions Bank [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Consolidated leverage ratio			5.00%
Loan Agreement [Member]
Line of Credit Facility [Line Items]
Related debt paid off			$ 12,000,000
Loan Agreement [Member] | Related To Regularly-Scheduled Principal Payments [Member]
Line of Credit Facility [Line Items]
Related debt paid off			5,000,000
Loan Agreement [Member] | Related To Various Requirements From Lenders [Member]
Line of Credit Facility [Line Items]
Related debt paid off			7,000,000
Loan Agreement [Member] | Non-Cash Activity [Member]
Line of Credit Facility [Line Items]
Decrease in consolidated indebtedness			$ 30,800,000
Jones Act [Member] | Subsequent Event [Member]
Line of Credit Facility [Line Items]
Related debt paid off	$ 700,000
Guarantees [Member]
Line of Credit Facility [Line Items]
Number of guaranteed separate loan facilities of two separate shipping companies | loan					2
Number of shipping companies indirectly owned by wholly-owned subsidiary | item					2
Guarantees [Member] | Loan Facility I [Member]
Line of Credit Facility [Line Items]
Guarantee obligation amount					$ 3,400,000
Guarantees [Member] | Loan Facility II [Member]
Line of Credit Facility [Line Items]
Guarantee obligation amount					$ 1,000,000
Handysize Vessel [Member]
Line of Credit Facility [Line Items]
Related debt paid off				13,500,000
Loss on Extinguishment of Debt				$ 95,000
Number of vessels sold | item			2	1
Capesize Bulk Carrier [Member]
Line of Credit Facility [Line Items]
Number of vessels sold | item			2
PCTC Vessels [Member]
Line of Credit Facility [Line Items]
Number of vessels under bareboat charter or lease agreements | item			2
Container Vessels [Member]
Line of Credit Facility [Line Items]
Number of vessels under operating contracts | item			2
Multi-purpose vessels [Member]
Line of Credit Facility [Line Items]
Number of vessels under operating contracts | item			2
2008 Mini-Bulk Carrier [Member]
Line of Credit Facility [Line Items]
Number of vessels under operating contracts | item			1
Deferred gains on sale of property			$ 8,100,000
Amortization expense slightly offset deferred gains			$ 900,000
Molten Sulphur Carrier [Member] | Jones Act [Member]
Line of Credit Facility [Line Items]
Number of vessels under bareboat charter or lease agreements | item			1
Tankers [Member]
Line of Credit Facility [Line Items]
Number of vessels under bareboat charter or lease agreements | item			2
Multi-Purpose Heavy Lift Vessel [Member] | Specialty Contracts [Member]
Line of Credit Facility [Line Items]
Number of vessels under bareboat charter or lease agreements | item			2
Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			$ 65,800,000
Minimum EBITDAR to fixed charge coverage ratio			1.05%
Consolidated minimum net worth			$ 228,000,000
Consolidated net income earned			50.00%
Percent of the proceeds of issuances of equity interests received			100.00%
Long term debt covenant minimum liquidity amount			$ 20,000,000
Credit Facility [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			31,000,000
Credit Facility [Member] | Letter of Credit [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			6,800,000
Credit Facility [Member] | Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit facility borrowing capacity			28,000,000
Old Line Of Credit Facility [Member] | Revolving Credit Facility [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit			40,000,000
Old Line Of Credit Facility [Member] | Standby Letters of Credit [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit			20,000,000
Old Line Of Credit Facility [Member] | Term Loan [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Debt instrument principal amount			45,000,000
Old Line Of Credit Facility [Member] | Swingline Loans [Member] | Regions Bank [Member]
Line of Credit Facility [Line Items]
Line of credit			$ 5,000,000