Derivative Instrument and Hedging Activities 4 Parentheticals (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Cash Flow Hedges Tax [Abstract]
Change in fair value of interest rate hedges tax	$ 6,891,000	$ 1,308,000	$ 7,757,000	$ 3,614,000
Reclassification of unrealized loss (gain) on interest rate hedges tax	2,253,000	2,250,000	4,481,000	4,554,000
Commodity Contracts Gathering and Processing Tax [Abstract]
Change in fair value of commodity hedges tax	(194,000)	390,000	365,000	(9,613,000)
Relcassification of unrealized (gain) loss on commodity hedges into earnings tax	1,678,000	1,830,000	3,310,000	2,272,000
Strategic Hedges [Abstract]
DerivativeCashReceivedOnHedge	7,300,000	9,000,000	16,800,000	20,000,000
Unrealized (gain) loss on commodity derivatives	$ (300,000)	$ (22,300,000)	$ 14,413,000	$ (16,654,000)