Acquisitions (Details 6) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended	12 Months Ended								6 Months Ended				6 Months Ended			6 Months Ended				0 Months Ended
	Sep. 30, 2013 Barges and tow boats	Mar. 31, 2013 Barges and tow boats	Sep. 30, 2013 Third Coast Towing, LLC	Sep. 30, 2013 Third Coast Towing, LLC Estimated Allocation	Mar. 31, 2013 Third Coast Towing, LLC Estimated Allocation	Sep. 30, 2013 Third Coast Towing, LLC Difference	Sep. 30, 2013 Third Coast Towing, LLC Trade names Estimated Allocation	Mar. 31, 2013 Third Coast Towing, LLC Trade names Estimated Allocation	Sep. 30, 2013 Third Coast Towing, LLC Trade names Difference	Sep. 30, 2013 Third Coast Towing, LLC Customer relationships	Sep. 30, 2013 Third Coast Towing, LLC Customer relationships Estimated Allocation	Mar. 31, 2013 Third Coast Towing, LLC Customer relationships Estimated Allocation	Sep. 30, 2013 Third Coast Towing, LLC Customer relationships Difference	Sep. 30, 2013 Third Coast Towing, LLC Barges and tow boats	Sep. 30, 2013 Third Coast Towing, LLC Barges and tow boats Estimated Allocation	Mar. 31, 2013 Third Coast Towing, LLC Barges and tow boats Estimated Allocation	Sep. 30, 2013 Third Coast Towing, LLC Other Minimum	Sep. 30, 2013 Third Coast Towing, LLC Other Maximum	Sep. 30, 2013 Third Coast Towing, LLC Other Estimated Allocation	Mar. 31, 2013 Third Coast Towing, LLC Other Estimated Allocation	Jan. 11, 2013 Third Coast Towing, LLC Call agreement Common units	Dec. 31, 2012 Third Coast Towing, LLC Call agreement Common units Minimum	Dec. 31, 2012 Third Coast Towing, LLC Call agreement Common units Maximum
Acquisitions
Number of common units issued to acquire business (in shares)																					344,680
Estimated fair value of the assets acquired and liabilities assumed
Accounts receivable - trade				$ 2,195	$ 2,248	$ (53)
Inventories				140	140
Property, plant and equipment															12,883	12,883			30	30
Useful life of property, plant and equipment	20 years	20 years												20 years			3 years	7 years
Intangible assets							850	500	350		3,000	4,000	(1,000)
Useful life of intangible assets										3 years
Goodwill				23,645	22,551	1,094
Other noncurrent assets				2,733	2,733
Trade accounts payable				(2,429)	(2,048)	(381)
Accrued expenses				(164)	(154)	(10)
Fair value of net assets acquired				42,883	42,883
Consideration paid for acquisition
Cash paid, net of cash acquired			35,000
Value of common units issued			7,883																		8,000	8,000	10,000
Total consideration paid			$ 42,883