Acquisitions (Details 3) (USD $)		12 Months Ended							12 Months Ended			12 Months Ended				0 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Barges and tow boats	Mar. 31, 2012 Barges and tow boats	Mar. 31, 2013 Common units	Mar. 31, 2012 Common units	Mar. 31, 2013 Third Coast	Dec. 31, 2012 Third Coast	Mar. 31, 2013 Third Coast Trade names	Mar. 31, 2013 Third Coast Customer relationships	Mar. 31, 2013 Third Coast Barges and tow boats	Mar. 31, 2013 Third Coast Other	Mar. 31, 2013 Third Coast Other Minimum	Mar. 31, 2013 Third Coast Other Maximum	Mar. 31, 2013 Third Coast Common units	Jan. 11, 2013 Third Coast Common units	Jan. 11, 2013 Third Coast Call agreement Common units	Dec. 31, 2012 Third Coast Call agreement Common units	Dec. 31, 2012 Third Coast Call agreement Common units Minimum	Dec. 31, 2012 Third Coast Call agreement Common units Maximum
Acquisitions
Number of common units issued to acquire ownership interests (in shares)				24,250,258	14,432,031									344,680		344,680
General and administrative expense						$ 300,000
Estimated fair value of the assets acquired and liabilities assumed
Accounts receivable							2,248,000
Other current assets							140,000
Property, plant and equipment										12,883,000	30,000
Useful life of property, plant and equipment		20 years	20 years							20 years		3 years	5 years
Intangible assets								500,000	4,000,000
Useful life of intangible assets									5 years
Goodwill							22,551,000
Other noncurrent assets							2,733,000
Assumed liabilities							(2,202,000)
Consideration paid, net of cash acquired							42,883,000
Consideration paid for acquisition
Cash paid, net of cash received pursuant to call agreement	14,000,000					35,000,000	35,000,000
Value of common units issued pursuant to call agreement														7,883,000	8,000,000		8,000,000	8,000,000	10,000,000
Total consideration paid						$ 42,883,000