Financial Instruments (Details 2)	3 Months Ended		6 Months Ended
	Jun. 30, 2013 bbl	Jun. 30, 2012 bbl	Jun. 30, 2013 bbl	Jun. 30, 2012 bbl
Schedule of Notional Quantities for Commodity Derivative Instruments
Sales of Notional Quantities of Oil and Gas	720,000	300,000	1,330,000	683,000
Purchases of Notional Quantities of Oil and Gas	615,000	235,000	1,290,000	686,000