LONG-TERM DEBT (Schedule of Long-term Debt) (Details) In Thousands, unless otherwise specified			3 Months Ended							3 Months Ended							0 Months Ended	3 Months Ended							3 Months Ended
	Jun. 30, 2012 USD ($)	Mar. 31, 2012 USD ($)	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] CAD	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] USD ($)	Mar. 31, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] USD ($)	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] Canadian Prime Rate [Member]	Mar. 31, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] Canadian Prime Rate [Member]	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] Canadian BA Rate [Member]	Mar. 31, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian term loan [Member] Canadian BA Rate [Member]	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] CAD	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] USD ($)	Mar. 31, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] USD ($)	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] Canadian Prime Rate [Member]	Mar. 31, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] Canadian Prime Rate [Member]	Jun. 30, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] Canadian BA Rate [Member]	Mar. 31, 2012 Lower Lakes Towing Ltd. [Member] Loans payable [Member] Canadian engine loan [Member] Canadian BA Rate [Member]	Dec. 01, 2011 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] USD ($)	Jun. 30, 2012 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] USD ($)	Mar. 31, 2012 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] USD ($)	Mar. 31, 2011 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member]	Jun. 30, 2012 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] LIBOR [Member]	Mar. 31, 2012 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] LIBOR [Member]	Jun. 30, 2012 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] US Base Rate [Member]	Mar. 31, 2012 Grand River Navigation Company, Inc. [Member] Loans payable [Member] US term loan [Member] US Base Rate [Member]	Jun. 30, 2012 Black Creek Holdings, Inc. [Member] Loans payable [Member] Black Creek US term loan [Member] USD ($)	Mar. 31, 2012 Black Creek Holdings, Inc. [Member] Loans payable [Member] Black Creek US term loan [Member] USD ($)	Jun. 30, 2012 Black Creek Holdings, Inc. [Member] Loans payable [Member] Black Creek US term loan [Member] LIBOR [Member]	Mar. 31, 2012 Black Creek Holdings, Inc. [Member] Loans payable [Member] Black Creek US term loan [Member] LIBOR [Member]	Jun. 30, 2012 Black Creek Holdings, Inc. [Member] Loans payable [Member] Black Creek US term loan [Member] US Base Rate [Member]	Mar. 31, 2012 Black Creek Holdings, Inc. [Member] Loans payable [Member] Black Creek US term loan [Member] US Base Rate [Member]
Long-term Debt, Current and Noncurrent [Abstract]
Long-term debt	$ 129,571	$ 133,601		$ 53,347	$ 55,386						$ 5,762	$ 6,015						$ 41,529	$ 42,233						$ 28,933	$ 29,967
Less amounts due within 12 months	9,599	9,686
Long-term debt, excluding current maturities	119,972	123,915
Basis spread on variable rate						3.50%	3.50%	4.50%	4.50%				4.00%	4.00%	5.00%	5.00%					4.50%	4.50%	3.50%	3.50%			4.75%	4.75%	3.75%	3.75%
Quarterly payment			936							133							$ 367	$ 704							$ 517
Effective interest rate including effect of interest rate swap contracts				6.91%	6.91%						6.31%	6.28%						6.21%	6.22%
Effective interest rate				5.81%	5.78%						6.31%	6.28%						4.97%		4.98%					5.22%	5.31%