Commitments and Contingencies (Details 2) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2011	Mar. 31, 2013	Mar. 31, 2012	Sep. 30, 2010 NGL Supply	Mar. 31, 2013 Natural gas liquids gal	Mar. 31, 2013 Crude oil bbl
Future minimum lease payments
2014		$ 55,065
2015		38,283
2016		31,297
2017		29,005
2018		21,520
Thereafter		36,268
Total		211,438
Sales and purchase contracts for natural gas liquids and crude oil
Rental expense	838	51,354	5,202	676
Fixed-price purchase commitments (in gallons)					84,159,000	3,382,000
Floating-price purchase commitments (in gallons)					540,518,000
Fixed-price sale commitments (in gallons)					102,071,000	5,642,000
Floating-price sale commitments (in gallons)					262,143,000
Fixed-price purchase commitments					76,386	303,819
Floating-price purchase commitments					604,584
Fixed-price sale commitments					100,246	504,505
Floating-price sale commitments					339,757
Amortization expense (income) recorded in cost of sales related to the forward purchase and sale contract assets and liabilities		13,498			14,587	(1,089)
Amortization expense (income) expected to be recorded in cost of sales related to the forward purchase and sale contract assets and liabilities ending next year		2,538			2,701	(163)
Amortization expense (income) included and expected to be recorded in cost of sales related to the forward purchase and sale contract assets and liabilities		16,036			17,288	(1,252)
Unamortized balances recorded in consolidated balance sheet
Current assets		3,124
Current liabilities		(586)
Net assets		$ 2,538