CONDENSED CONSOLIDATED BALANCE SHEETS Parenthetical (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Assets Held-for-sale [Member]	Dec. 31, 2011 Assets Held-for-sale [Member]	Dec. 31, 2012 Other Capitalized Property Plant and Equipment [Member]	Dec. 31, 2011 Other Capitalized Property Plant and Equipment [Member]	Dec. 31, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 2,376,170,000	$ 1,766,445,000	$ 20,676,000	$ 10,714,000	$ 22,442,000	$ 23,985,000
Debt Instrument, Interest Rate, Stated Percentage							3.50%	3.50%
3.50% Convertible Notes, unamortized discount							$ 0	$ 2,431,000
Common Stock, Par Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Issued	66,245,816	64,145,482
Common Stock, Shares, Outstanding	66,195,235	64,064,415
Treasury Stock, Shares	50,581	81,067