CHANGES IN ACCOUNTING ESTIMATES (Details) (USD $)		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010 Extended Economic Life on U.S. Flag Coal Carrier [Member]	Dec. 31, 2010 Extended Economic Life of Both Mobile Alabama and Coatzacoalcos [Member]	Dec. 31, 2010 Extended Economic Life of Both Mobile Alabama and Coatzacoalcos [Member] Alabama, United States [Member]	Dec. 31, 2010 Extended Economic Life of Both Mobile Alabama and Coatzacoalcos [Member] Coatzacoalcos, Mexico [Member]	Dec. 31, 2012 Change in Salvage Value [Member]
CHANGES IN ACCOUNTING ESTIMATES [Abstract]
Period between salvage value reviews	3 years
Period used to determine reasonableness of salvage values	3 years
Change in Accounting Estimate [Line Items]
Number of vessels for which salvage values were adjusted						8
Average remaining useful lives of vessels						9 years
Decrease in future depreciation expense						$ 3,800,000
Increase in pre-tax income		5,200,000	1,800,000			3,780,000
Increase in net income		$ 3,400,000	$ 1,200,000			$ 3,780,000
Increase in basic earnings per share (in dollars per share)		$ 0.47	$ 0.16			$ 0.53
Increase in diluted earnings per share (in dollars per share)		$ 0.47	$ 0.16			$ 0.53
Extended amortization period of assets				2 years 6 months	6 years