Divestitures and Discontinued Operations Additional Information (Details) (USD $)		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013 Piceance and NECO Asset Group	Jun. 30, 2012 Permian Basin Asset Group
Additional Disclosures
Oil and gas assets sale price before adjustments ($ in millions)			$ 173,900,000
Proceeds from Sale of Oil and Gas Property and Equipment ($ in millions)		177,600,000	189,200,000
Proceeds To NonAffiliated Investor Partners		17,000,000
Pre-tax loss on sale of crude oil and gas properties		$ (1,100,000)
Appalachian Basin Wells Held for Sale	3,500