Derivative Instruments (Details 2) (Not Designated as Hedging Instrument, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Current liabilities:
Total	$ 2,218
Commodity Derivatives | Assets from price risk management - current
ASSETS
Fair value, asset	3,222
Commodity Derivatives | Assets from price risk management - long term
ASSETS
Fair value, asset	177
Commodity Derivatives | Liabilities from price risk management - current
Current liabilities:
Fair value, liability	(648)
Interest Rate Swap | Other current liabilities
Current liabilities:
Fair value, liability	(222)
Interest Rate Swap | Other long term liabilities
Current liabilities:
Fair value, liability	$ (311)