Fair Value Measurements (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Assets
Total assets	$ 25,755	$ 27,752
Liabilities
Transfer out of Level 2	0	0	0
Transfer out of Level 2	0	0	0
Non-financial assets	0	0
Non-financial liabilities	0	0
Commodity derivatives
Assets
Total assets	23,199	26,976
Currency derivatives
Assets
Total assets	2,556	776
Recurring | Level 2
Assets
Total assets	25,755	27,752
Liabilities
Long-term debt	570,700	669,500
Total liabilities	602,014	694,079
Recurring | Level 2 | Commodity derivatives
Assets
Total assets	23,199	26,976
Liabilities
Total liabilities	31,154	24,269
Recurring | Level 2 | Currency derivatives
Assets
Total assets	2,556	776
Liabilities
Total liabilities	160	310
Recurring | Total
Assets
Total assets	25,755	27,752
Liabilities
Long-term debt	570,700	669,500
Total liabilities	602,014	694,079
Recurring | Total | Commodity derivatives
Assets
Total assets	23,199	26,976
Liabilities
Total liabilities	31,154	24,269
Recurring | Total | Currency derivatives
Assets
Total assets	2,556	776
Liabilities
Total liabilities	$ 160	$ 310