Financial Instruments and Risk Management (Derivative Instruments by Income Statement Location) (Details) (USD $)	3 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Derivative Instruments, Gain (Loss) [Line Items]
Net gain recognized in OCI on derivative (effective portion), net of tax of $41.4 million, and $19.5 million			$ 67,547,000	$ 31,801,000	$ (3,316,000)
Net gain recognized in OCI on derivative (effective portion), Tax	41,400,000	19,500,000	41,399,000	19,491,000	(2,032,000)
Deferred net gains (losses) on derivative instruments recoreded in AOCI, net of tax, expected to be reclasses during next 12 months			(2,500,000)
Not Designated as Hedging Instrument | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Loss recongnized in income on derivative			(37,587,000)	(3,000)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Net gain recognized in OCI on derivative (effective portion), net of tax of $41.4 million, and $19.5 million			67,546,000	31,801,000
Designated as Hedging Instrument | Operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain reclassified from accumulated OCI into income (effective portion)			26,326,000	200,000
Gain (loss) recognized in income on derivative (ineffective portion and amount excluded from effectiveness testing)			$ (2,767,000)	$ 1,000