Hedge Contracts (Tables) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Derivative Swap Contracts, Oil
Amount of pretax gain reclassified from accumulated other comprehensive income into product sales revenue (effective portion)	$ 0	$ 4,858	$ 1,177	$ 9,939
Amount of pretax gain (loss) from change in derivative fair value recognized in other comprehensive income	0	(11,097)	(7,854)	(9,320)
Amount of pretax gain (loss) recognized in other income (expense) (ineffective portion)	(14,224)	419	(13,947)	125
Derivative Swap Contracts, Natural Gas
Amount of pretax gain reclassified from accumulated other comprehensive income into product sales revenue (effective portion)	0	7,725	0	12,225
Amount of pretax gain (loss) from change in derivative fair value recognized in other comprehensive income	0	1,371	0	(7,287)
Amount of pretax gain (loss) recognized in other income (expense) (ineffective portion)	0	(35)	0	215
Derivative Swap Contracts, Total
Amount of pretax gain reclassified from accumulated other comprehensive income into product sales revenue (effective portion)	0	12,583	1,177	22,164
Amount of pretax gain (loss) from change in derivative fair value recognized in other comprehensive income	0	(9,726)	(7,854)	(16,607)
Amount of pretax gain (loss) recognized in other income (expense) (ineffective portion)	$ (14,224)	$ 384	$ (13,947)	$ 340