Derivative Financial Instruments (Schedule Of Notional Amounts And Estimated Fair Values Of Commodity Derivative Positions) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Non-Hedging Commodity Swaps [Member]
Derivative Instruments [Line Items]
Notional Units, Barrels	Barrels
Notional Units, Barrels	Barrels
Notional Units, MMBTUs	MMBTUs
Notional Units, MMBTUs	MMBTUs
Non-Hedging Commodity Swaps [Member] | Fair Value [Member]
Derivative Instruments [Line Items]
Oil Barrels In Dollars	$ 504	$ 1,068
Oil Barrels (2)In Dollars	(401)	(963)
Natural gas MMBTUs In Dollars	236	3,540
Natural gas MMBTUs (2) In Dollars	(222)	(3,480)
Non-Hedging Commodity Swaps [Member] | Notional Amount [Member]
Derivative Instruments [Line Items]
Oil Barrels	508,000	459,000
Oil Barrels (2)	508,000	459,000
Natural gas MMBTUs	830,000	1,905,000
Natural gas MMBTUs (2)	830,000	1,905,000
Non-Hedging Commodity Options [Member]
Derivative Instruments [Line Items]
Notional Units, Barrels	Barrels
Notional Units, Barrels	Barrels
Notional Units, MMBTUs	MMBTUs
Notional Units, MMBTUs	MMBTUs
Non-Hedging Commodity Options [Member] | Fair Value [Member]
Derivative Instruments [Line Items]
Oil Barrels In Dollars	5,830	18,206
Oil Barrels (2)In Dollars	(5,830)	(18,206)
Natural gas MMBTUs In Dollars	180	490
Natural gas MMBTUs (2) In Dollars	$ (180)	$ (490)
Non-Hedging Commodity Options [Member] | Notional Amount [Member]
Derivative Instruments [Line Items]
Oil Barrels	1,410,000	2,920,000
Oil Barrels (2)	1,410,000	2,920,000
Natural gas MMBTUs	360,000	480,000
Natural gas MMBTUs (2)	360,000	480,000