Derivative Instrument and Hedging Activities 4 Parentheticals (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash Flow Hedges Tax [Abstract]
Change in fair value of interest rate hedges tax	$ 27,589,000	$ 5,237,000	$ 3,051,000
Reclassification of unrealized loss (gain) on interest rate hedges tax	9,012,000	9,019,000	8,222,000
Commodity Contracts Gathering and Processing Tax [Abstract]
Change in fair value of commodity hedges tax	(2,598,000)	(14,093,000)	(3,773,000)
Relcassification of unrealized gain (loss) on commodity hedges into earnings tax	8,536,000	6,787,000	16,231,000
Strategic Hedges [Line Items]
Unrealized loss on commodity derivatives	50,000	18,514,000	44,778,000
Gathering And Processing [Member]
Strategic Hedges [Line Items]
Derivative Cash Received On Hedge	29,100,000	34,500,000	59,700,000
Unrealized loss on commodity derivatives		$ (18,600,000)	$ (44,900,000)