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Derivative Instruments (Details Textual) (USD $)	3 Months Ended
Derivative Instruments (Details Textual) (USD $)	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments (Textual) [Abstract]
Realization of gain, net of taxes	$ (2,000,000)
Gas hedges [Member]
Derivative Instruments (Textual) [Abstract]
Gain or loss recognized in oil and gas contracts	532,000	2,155,000
Crude Oil [Member]
Derivative Instruments (Textual) [Abstract]
Gain or loss recognized in oil and gas contracts	$ (145,000)	$ (53,000)

The amount of net gains and losses recognized in income during the period on derivative instruments designated and qualifying as hedging instruments in fair value hedges and related hedged items designated and qualifying in fair value hedges, on derivative instruments designated and qualifying as hedging instruments in cash flow hedges, and on derivative instruments not designated as hedging instruments.

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