Financial Instruments and Risk Management (WTI Open Contracts) (Details)	9 Months Ended		12 Months Ended
	Sep. 30, 2015 bbl / d $ / bbl	Sep. 30, 2014 bbl / d $ / bbl	Dec. 31, 2016 bbl / d $ / bbl
October - December 2015 [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day) | bbl / d	15,000
Swap Prices	63.30
October - December 2014 [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day) | bbl / d		22,000
Swap Prices		93.26
Scenario, Forecast [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day) | bbl / d			20,000
Swap Prices			52.01