Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 97,615	$ 83,275	$ 23,003	$ 15,166	$ 16,632	$ 10,302	$ 19,053	$ 14,104	$ 219,058	$ 60,091	$ 71,675
Operating expenses	59,857	64,174	41,359	33,867	50,800	42,524	18,304	16,077	58,536	17,668	15,347
Income (Loss) From Operations	37,758	19,101	(18,356)	(18,701)	(34,168)	(32,222)	749	(1,973)	19,801	(67,614)	1,327
Net Income (Loss) to Common Shareholders	(6,910)	(34,158)	(51,264)	(35,718)	(45,101)	(63,756)	(16,110)	(8,002)	(128,049)	(132,969)	54,304
Impairment of oil and gas properties	$ 6,000	$ 11,400	$ 20,000	$ 15,700	$ 36,900	$ 28,800	$ 0	$ 0	$ 53,072	$ 65,706	$ 7,692
Earnings Per Share Basic And Diluted [Abstract]
Earnings Per Share Basic	$ (0.15)	$ (0.73)	$ (1.31)	$ (0.94)	$ (1.15)	$ (1.63)	$ (0.42)	$ (0.30)	$ (3.01)	$ (3.70)	$ 2.34
Earnings Per Share Diluted	$ (0.15)	$ (0.73)	$ (1.31)	$ (0.94)	$ (1.15)	$ (1.63)	$ (0.42)	$ (0.30)	$ (3.01)	$ (3.70)	$ 1.95