Derivative Financial Instruments (Schedule Of Notional Amounts And Estimated Fair Values Of Commodity Derivative Positions) (Details) (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Notional Amount [Member] | Non-Hedging Commodity Swaps [Member]
Oil commodity	$ 525	$ 321
Natural gas commodity (2)	3,105	510
Natural gas commodity	3,105	510
Oil commodity (2)	525	321
Notional Amount [Member] | Non-Hedging Commodity Options [Member]
Oil commodity	2,639	1,288
Natural gas commodity (2)	1,440	3,820
Natural gas commodity	1,440	3,820
Oil commodity (2)	2,639	1,288
Estimated Fair Value [Member] | Non-Hedging Commodity Swaps [Member]
Oil commodity	6,947	2,502
Natural gas commodity (2)	(2,724)	(174)
Natural gas commodity	2,816	195
Oil commodity (2)	(6,829)	(2,428)
Estimated Fair Value [Member] | Non-Hedging Commodity Options [Member]
Oil commodity	21,605	7,706
Natural gas commodity (2)	(1,549)	(3,774)
Natural gas commodity	1,549	3,774
Oil commodity (2)	$ (21,605)	$ (7,706)
Non-Hedging Commodity Swaps [Member]
Notional Units, MMBTUs (2)	MMBTUs
Notional Units, MMBTUs	MMBTUs
Notional Units, barrels (2)	Barrels
Notional Units, barrels	Barrels
Non-Hedging Commodity Options [Member]
Notional Units, MMBTUs (2)	MMBTUs
Notional Units, MMBTUs	MMBTUs
Notional Units, barrels (2)	Barrels
Notional Units, barrels	Barrels