Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Assets
Total assets at fair value	$ 3,399
Liabilities
Total liabilities at fair value	(1,181)
Commodity Forward Contracts
Assets
Derivative Instruments	3,399
Liabilities
Derivative Instruments	(648)
Interest Rate Swap
Liabilities
Derivative Instruments	(533)
Level 1
Assets
Total assets at fair value
Liabilities
Total liabilities at fair value
Level 1 | Commodity Forward Contracts
Assets
Derivative Instruments
Liabilities
Derivative Instruments
Level 1 | Interest Rate Swap
Liabilities
Derivative Instruments
Level 2
Assets
Total assets at fair value	3,399
Liabilities
Total liabilities at fair value	(1,181)
Level 2 | Commodity Forward Contracts
Assets
Derivative Instruments	3,399
Liabilities
Derivative Instruments	(648)
Level 2 | Interest Rate Swap
Liabilities
Derivative Instruments	(533)
Level 3
Assets
Total assets at fair value
Liabilities
Total liabilities at fair value
Level 3 | Commodity Forward Contracts
Assets
Derivative Instruments
Liabilities
Derivative Instruments
Level 3 | Interest Rate Swap
Liabilities
Derivative Instruments