Risk Management Activities and Financial Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Fair value of risk management assets and liabilities
Short-term risk management assets	$ 27,208	$ 21,159
Long-term risk management assets	6,521	6,593
Short-term risk management liabilities	(19,000)	(20,005)
Long-term risk management liabilities	(5,071)	(4,574)
Total	9,658	3,173
Not designated as hedge
Fair value of risk management assets and liabilities
Short-term risk management assets	27,208	21,159
Long-term risk management assets	6,521	6,593
Short-term risk management liabilities	(19,000)	(20,005)
Long-term risk management liabilities	(5,071)	(4,574)
Total	9,658	3,173
Energy Contracts
Fair value of risk management assets and liabilities
Total	9,562
Energy Contracts | Not designated as hedge
Fair value of risk management assets and liabilities
Short-term risk management assets	27,076	20,383
Long-term risk management assets	6,426	6,593
Short-term risk management liabilities	(18,869)	(19,792)
Long-term risk management liabilities	(5,071)	(4,477)
Total	9,562	2,707
Currency contracts
Fair value of risk management assets and liabilities
Total	96
Currency contracts | Not designated as hedge
Fair value of risk management assets and liabilities
Short-term risk management assets	132	776
Long-term risk management assets	95
Short-term risk management liabilities	(131)	(213)
Long-term risk management liabilities		(97)
Total	$ 96	$ 466