Derivative Financial Instruments (Schedule Of Notional Amounts And Estimated Fair Values Of Commodity Derivative Positions) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Non-Hedging Commodity Swaps [Member]
Derivative Instruments [Line Items]
Notional Units, MMBTUs	MMBTUs
Notional Units, MMBTUs (2)	MMBTUs
Notional Units, Barrels	Barrels
Notional Units, Barrels (2)	Barrels
Non-Hedging Commodity Options [Member]
Derivative Instruments [Line Items]
Notional Units, MMBTUs	MMBTUs
Notional Units, MMBTUs (2)	MMBTUs
Notional Units, Barrels	Barrels
Notional Units, Barrels (2)	Barrels
Notional Amount [Member] | Non-Hedging Commodity Swaps [Member]
Derivative Instruments [Line Items]
Oil commodity	$ 521	$ 459
Oil commodity (2)	521	459
Natural gas commodity	990	1,905
Natural gas commodity (2)	990	1,905
Notional Amount [Member] | Non-Hedging Commodity Options [Member]
Derivative Instruments [Line Items]
Oil commodity	2,610	2,920
Oil commodity (2)	2,610	2,920
Natural gas commodity	600	480
Natural gas commodity (2)	600	480
Estimated Fair Value [Member] | Non-Hedging Commodity Swaps [Member]
Derivative Instruments [Line Items]
Oil commodity	2,505	1,068
Oil commodity (2)	(2,387)	(963)
Natural gas commodity	2,321	3,540
Natural gas commodity (2)	(2,289)	(3,480)
Estimated Fair Value [Member] | Non-Hedging Commodity Options [Member]
Derivative Instruments [Line Items]
Oil commodity	12,327	18,206
Oil commodity (2)	(12,327)	(18,206)
Natural gas commodity	581	490
Natural gas commodity (2)	$ (581)	$ (490)