Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Fair value of risk management assets and liabilities
Short-term risk management assets	$ 20,949	$ 21,159
Long-term risk management assets	4,806	6,593
Short-term risk management liabilities	(19,105)	(20,005)
Long-term risk management liabilities	(12,209)	(4,574)
Total	(5,559)	3,173
Not designated as hedge
Fair value of risk management assets and liabilities
Short-term risk management assets	20,949	21,159
Long-term risk management assets	4,806	6,593
Short-term risk management liabilities	(19,105)	(20,005)
Long-term risk management liabilities	(12,209)	(4,574)
Total	(5,559)	3,173
Energy Contracts
Fair value of risk management assets and liabilities
Total	(7,955)
Energy Contracts | Not designated as hedge
Fair value of risk management assets and liabilities
Short-term risk management assets	18,939	20,383
Long-term risk management assets	4,260	6,593
Short-term risk management liabilities	(18,945)	(19,792)
Long-term risk management liabilities	(12,209)	(4,477)
Total	(7,955)	2,707
Currency contracts
Fair value of risk management assets and liabilities
Total	2,396
Currency contracts | Not designated as hedge
Fair value of risk management assets and liabilities
Short-term risk management assets	2,010	776
Long-term risk management assets	546
Short-term risk management liabilities	(160)	(213)
Long-term risk management liabilities		(97)
Total	$ 2,396	$ 466