Summary of Significant Accounting Policies, Derivatives by Hedging Relationship and Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified											3 Months Ended
	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 1 Quoted Prices [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 1 Quoted Prices [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 2 Observable [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 2 Observable [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Level 3 Unobservable [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Level 3 Unobservable [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Counterparty Offsets [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Counterparty Offsets [Member]	Mar. 31, 2013 Fair Value, Measurements, Recurring [Member] Total Fair Value [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member] Total Fair Value [Member]	Mar. 31, 2013 Commodity Contract [Member] Revenues - marketing [Member] Not Designated as Hedging Instrument [Member]	Mar. 31, 2012 Commodity Contract [Member] Revenues - marketing [Member] Not Designated as Hedging Instrument [Member]
Earnings (loss) recognized in income [Abstract]
Earnings (Loss)											$ 254	$ (2,882)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	510	299	398	389	0	0	(146)	(270)	762	418
Derivatives - Current liabilities	0	0	(648)	(682)	0	0	146	270	(502)	(412)
Net Value	$ 510	$ 299	$ (250)	$ (293)	$ 0	$ 0	$ 0	$ 0	$ 260	$ 6