Derivative Instruments (Details 2) (Not Designated as Hedging Instrument, USD $) In Thousands, unless otherwise specified	Sep. 30, 2013
Current liabilities:
Total	$ 3,783
Commodity Derivatives | Assets from price risk management - current
ASSETS
Fair value, asset	3,182
Commodity Derivatives | Assets from price risk management - long term
ASSETS
Fair value, asset	951
Commodity Derivatives | Liabilities from price risk management - current
Current liabilities:
Fair value, liability	(8)
Interest Rate Swap | Other current liabilities
Current liabilities:
Fair value, liability	(219)
Interest Rate Swap | Other long term liabilities
Current liabilities:
Fair value, liability	$ (123)