Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
Assets
Total assets	$ 44,677	$ 27,752
Liabilities
Total liabilities	21,388	24,579
Total	23,289	3,173
Commodity derivatives
Assets
Total assets	43,170	26,976
Liabilities
Total liabilities	21,375	24,269
Total	21,795	2,707
Currency derivatives
Assets
Total assets	1,507	776
Liabilities
Total liabilities	13	310
Total	1,494	466
Recurring | Level 2
Assets
Total assets	44,677	27,752
Liabilities
Total liabilities	21,388	24,579
Total	23,289	3,173
Recurring | Level 2 | Commodity derivatives
Assets
Total assets	43,170	26,976
Liabilities
Total liabilities	21,375	24,269
Recurring | Level 2 | Currency derivatives
Assets
Total assets	1,507	776
Liabilities
Total liabilities	13	310
Recurring | Total
Assets
Total assets	44,677	27,752
Liabilities
Total liabilities	21,388	24,579
Total	23,289	3,173
Recurring | Total | Commodity derivatives
Assets
Total assets	43,170	26,976
Liabilities
Total liabilities	21,375	24,269
Recurring | Total | Currency derivatives
Assets
Total assets	1,507	776
Liabilities
Total liabilities	$ 13	$ 310