Acquisitions (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Oct. 28, 2012	Oct. 26, 2012	Sep. 30, 2012 Prize [Member]	Sep. 30, 2012 Prize [Member]	Apr. 20, 2012 Prize [Member]	Dec. 31, 2011 Prize [Member]
Business Acquisition [Line Items]
Date of acquisition								Apr. 20, 2012
Cash paid for acquisition									$ 225,000,000
Effective date of acquisition								Jan. 01, 2012
Estimated proved reserves (BOE)										13,300,000
Cost associated with acquisition recorded in acquisition and transaction costs								1,000,000
Estimated environmental liability							1,900,000	1,900,000	1,891,000
Revenue	64,969,000	64,781,000	192,965,000	195,492,000			8,700,000	15,200,000
Operating expenses	56,404,000	53,183,000	165,152,000	148,102,000			3,400,000	6,100,000
Approximate cash payment for oil and gas properties in Akr-La- Tex region					$ 215,000,000	$ 215,000,000