Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Assets
Total assets	$ 33,729	$ 27,752
Liabilities
Total liabilities	24,071	24,579
Total	9,658	3,173
Commodity derivatives
Assets
Total assets	33,503	26,976
Liabilities
Total liabilities	23,940	24,269
Total	9,562
Currency derivatives
Assets
Total assets	226	776
Liabilities
Total liabilities	131	310
Total	96
Recurring | Level 2
Assets
Total assets	33,729	27,752
Liabilities
Total liabilities	24,071	24,579
Total	9,658	3,173
Recurring | Level 2 | Commodity derivatives
Assets
Total assets	33,503	26,976
Liabilities
Total liabilities	23,940	24,269
Recurring | Level 2 | Currency derivatives
Assets
Total assets	226	776
Liabilities
Total liabilities	131	310
Recurring | Total
Assets
Total assets	33,729	27,752
Liabilities
Total liabilities	24,071	24,579
Total	9,658	3,173
Recurring | Total | Commodity derivatives
Assets
Total assets	33,503	26,976
Liabilities
Total liabilities	23,940	24,269
Recurring | Total | Currency derivatives
Assets
Total assets	226	776
Liabilities
Total liabilities	$ 131	$ 310