Summary of Significant Accounting Policies Other (Details) (USD $)	12 Months Ended						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Regency Gas Services, LLC [Member]	Dec. 31, 2012 Plains Marketing, LP [Member]	Dec. 31, 2012 Moody's, Baa2 Rating [Member]	Dec. 31, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]	Dec. 31, 2010 Convertible Debt [Member]	Feb. 14, 2013 Line of Credit [Member]	Dec. 31, 2012 Line of Credit [Member]	Dec. 31, 2011 Line of Credit [Member]
Basis of Presentation and Significant Accounting Policies [Line Items]
Long-term credit facility	$ 340,000,000	$ 0								$ 407,500,000	$ 340,000,000	$ 0
Concentration of Credit Risk and Major Customers [Abstract]
Number of Major Customers	2
Entity-Wide Revenue, Major Customer, Percentage		18.00%	11.00%	21.10%	13.40%
Number of Counterparties Downgraded	2
Number of Derivative Counterparties	10					9
Property, Plant and Equipment [Abstract]
Property, Plant, and Equipment, Salvage Value	64,400,000	64,100,000
Inventory, Net [Abstract]
Raw Materials Inventory	13,400,000	16,500,000
Property, Plant and Equipment, Estimated Useful Lives	three to thirty years
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, Net (Excluding Goodwill)	10,800,000	7,100,000
Cash Settlement Balancing [Abstract]
Gas Balancing Receivable	1,700,000	1,900,000
Gas Balancing Payable	1,300,000	1,100,000
Revenues [Abstract]
Revenue Receipt, Days After Sale, Low End of Range	30
Revenue Receipt, Days After Sale, High End of Range	90
Impairment of Proved Properties [Abstract]
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast	5
Impairment of proved properties	208,923,000	219,037,000	6,127,000
Abandonment and impairment of unproved properties	16,342,000	7,367,000	1,986,000
Debt Instruments [Abstract]
Debt Instrument, Interest Rate, Stated Percentage							3.50%	3.50%	3.50%
Debt Instrument, Convertible, Conversion Price							$ 54.42
Debt Instrument, Principal Amount Denominator for Conversion into Common Stock							$ 1,000
Debt instrument convertible conversion rate							864,106