Derivative Instruments (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current liabilities:
Total	$ (2,035)	$ (422)
Commodity Derivatives
ASSETS
Fair value, asset	694	620
Commodity Derivatives | Assets from price risk management - current
ASSETS
Fair value, asset		218
Commodity Derivatives | Assets from price risk management - long term
ASSETS
Fair value, asset	694	402
Commodity Derivatives | Liabilities from price risk management - current
Current liabilities:
Fair value, liability	(1,626)	(13)
Commodity Derivatives | Liabilities from price risk management - long term
Current liabilities:
Fair value, liability	(134)	(97)
Interest Rate Swap | Other current liabilities
Current liabilities:
Fair value, liability	(231)	(222)
Interest Rate Swap | Other long term liabilities
Current liabilities:
Fair value, liability	$ (44)	$ (90)