Financial Instruments and Risk Management (WTI Open Contracts) (Details) - Commodity Derivative Contracts [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 2015 bbl / d $ / bbl	Dec. 31, 2014 bbl / d $ / bbl
July - September 2015 [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day)	15,000
Swap Prices | $ / bbl	62.84
October - December 2015 [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day)	15,000
Swap Prices | $ / bbl	63.30
July - September 2014 [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day)		26,000
Swap Prices | $ / bbl		94.89
October - December 2014 [Member]
Oil and Gas Delivery Commitments and Contracts [Line Items]
Volumes (barrels per day)		16,000
Swap Prices | $ / bbl		92.33