Acquisitions (Details 8) (USD $)		12 Months Ended			12 Months Ended			0 Months Ended			0 Months Ended				0 Months Ended					12 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Common units	Mar. 31, 2012 Common units	Nov. 01, 2011 NGL Energy Holdings, LLC SemStream	Mar. 31, 2012 SemStream	Nov. 01, 2011 SemStream item bbl gal	Nov. 01, 2011 SemStream Customer relationships	Nov. 01, 2011 SemStream Customer relationships Minimum	Nov. 01, 2011 SemStream Customer relationships Maximum	Nov. 01, 2011 SemStream Rail car leases	Nov. 01, 2011 SemStream Rail car leases Minimum	Nov. 01, 2011 SemStream Rail car leases Maximum	Nov. 01, 2011 SemStream Land	Nov. 01, 2011 SemStream Tanks and terminals	Nov. 01, 2011 SemStream Tanks and terminals Minimum	Nov. 01, 2011 SemStream Tanks and terminals Maximum	Nov. 01, 2011 SemStream Vehicles and rail cars	Nov. 01, 2011 SemStream Other	Nov. 01, 2011 SemStream Common units	Mar. 31, 2012 SemStream Common units
Acquisitions
Number of common units issued to acquire ownership interests (in shares)		24,250,258	14,432,031																8,932,031	8,932,031
Cash paid to acquire ownership interests	$ 14,000,000					$ 91,000,000
Value of common units issued to acquire ownership interests																			184,800,000
Issue price of units (in dollars per unit)																			$ (21.07)
Ownership interest acquired in general partner (as a percent)				7.50%
General and administrative expense					736,000
Equity issuance costs					43,000
Number of acquired natural gas liquids terminals						12
Volume of acquired above ground propane storage (in gallons)						12,000,000
Volume of acquired underground leased storage (in barrels)						3,700,000
Number of owned rail cars						350
Number of leased rail cars						12
Estimated fair value of the assets acquired and liabilities assumed
Propane and other natural gas liquids inventory						104,226,000
Derivative financial instruments						3,578,000
Assets held for sale						3,000,000
Prepaids and other current assets						9,833,000
Property, plant and equipment													3,470,000	41,434,000			470,000	3,326,000
Useful life of property, plant and equipment															20 years	30 years	5 years	5 years
Investment in capital lease						3,112,000
Amortizable intangible assets							31,950,000			1,008,000
Useful life of intangible assets								8 years	15 years		1 year	4 years
Goodwill						74,924,000
Assumed current liabilities						(4,591,000)
Consideration paid, net of cash acquired						$ 275,740,000