Risk Management Activities and Financial Instruments (Details 3) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Assets
Gross Amounts Recognized	$ 117,156	$ 89,563
Gross Amounts Offset in the Balance Sheets	(83,427)	(61,811)
Net Amounts Presented in the Balance Sheets	33,729	27,752
Margin Deposits not Offset in the Balance Sheets	(23,170)	(15,806)
Net Amounts	10,559	11,946
Liabilities
Gross Amounts Recognized	107,498	86,390
Gross Amounts offset in the Balance Sheets	(83,427)	(61,811)
Net Amounts Presented in the Balance Sheets	24,071	24,579
Margin Deposits not Offset in the Balance Sheets	(16,564)	(17,025)
Net Amounts	7,507	7,554
Net - Amounts Presented in the Balance Sheets	9,658	3,173
Net - Margin Deposits not Offset in the Balance Sheets	(6,606)	1,219
Net	3,052	4,392
Commodity derivatives
Assets
Gross Amounts Recognized	116,883	88,682
Gross Amounts Offset in the Balance Sheets	(83,380)	(61,706)
Net Amounts Presented in the Balance Sheets	33,503	26,976
Margin Deposits not Offset in the Balance Sheets	(22,944)	(15,030)
Net Amounts	10,559	11,946
Liabilities
Gross Amounts Recognized	107,320	85,975
Gross Amounts offset in the Balance Sheets	(83,380)	(61,706)
Net Amounts Presented in the Balance Sheets	23,940	24,269
Margin Deposits not Offset in the Balance Sheets	(16,433)	(16,861)
Net Amounts	7,507	7,408
Net - Amounts Presented in the Balance Sheets	9,562
Currency contracts
Assets
Gross Amounts Recognized	273	881
Gross Amounts Offset in the Balance Sheets	(47)	(105)
Net Amounts Presented in the Balance Sheets	226	776
Margin Deposits not Offset in the Balance Sheets	(226)	(776)
Liabilities
Gross Amounts Recognized	178	415
Gross Amounts offset in the Balance Sheets	(47)	(105)
Net Amounts Presented in the Balance Sheets	131	310
Margin Deposits not Offset in the Balance Sheets	(131)	(164)
Net Amounts		146
Net - Amounts Presented in the Balance Sheets	$ 96