Derivatives (Narrative) (Details) (USD $)	12 Months Ended			0 Months Ended	7 Months Ended	12 Months Ended		17 Months Ended	0 Months Ended	17 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jul. 28, 2009 Costless Collar [Member]	Jul. 31, 2011 Costless Collar [Member]	Dec. 31, 2012 Costless Collar [Member]	Dec. 31, 2011 Costless Collar [Member]	Dec. 31, 2010 Costless Collar [Member]	Jun. 27, 2011 Cargill Agreement [Member]	Dec. 31, 2012 Cargill Agreement [Member]
Derivative [Line Items]
Price agreement term				two					If the average price falls below $65 per barrel, then Cargill will pay to the Company the difference between $65 and the lower average price for 10,000 barrels per month in each month during when such lower average prices occur.
Floor price (per barrel)				60.00					65
Cap price (per barrel)				81.50
Monthly volume (in barrels)					7,375			9,500		10,000
Difference per barrel of Kansas Common plus bonus and current WTI NYMEX						7
Contract description				two					If the average price falls below $65 per barrel, then Cargill will pay to the Company the difference between $65 and the lower average price for 10,000 barrels per month in each month during when such lower average prices occur.
Derivative issuance cost per barrel									2.20
Payments of derivative issuance costs									$ 374,000
Unrealized gain (loss) on derivatives	140,000	450,000	630,000
Settlement payments			$ 130,000				$ 860,000