Summarized Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]
Revenues from continuing operations	$ 189,301	$ 222,503	$ 207,998	$ 219,309	$ 319,050	$ 288,608	$ 296,063	$ 326,299	$ 839,111	$ 1,230,020	$ 933,404
Gain (loss) on commodity derivatives	2	9,390	(3,646)	36,865	110,725	32,052	(15,102)	(45,273)	42,611	82,402	(46,754)
Expenses from continuing operations	207,452	195,339	188,483	189,347	195,083	169,669	150,850	154,829	780,621	670,431
Ceiling test and other impairments	3,144,899	0	0	0					3,144,899	0	0
Interest expense	43,494	43,137	42,619	42,668	42,196	29,599	27,294	27,068	171,918	126,157	101,486
Gain on sale of property					8,022	0	0	0	0	8,022	0
Other (expense) income, net	903	2,354	1,827	(992)	5,311	2,582	2,688	2,590	4,092	13,171
Income (loss) from continuing operations	(3,205,639)	(4,229)	(24,923)	23,167	205,829	123,974	105,505	101,719	(3,211,624)	537,027	234,222
Income tax (benefit)	(999)	(1,133)	(250)	(2,022)	(3,901)	(1,383)	(544)	4	(4,404)	(5,824)	(3,616)
Net income (loss)	$ (3,204,640)	$ (3,096)	$ (24,673)	$ 25,189	$ 209,730	$ 125,357	$ 106,049	$ 101,715	$ (3,207,220)	$ 542,851	$ 237,838
Net (income (loss) per common share - basic	$ (20.91)	$ (0.02)	$ (0.16)	$ 0.16	$ 1.37	$ 0.82	$ 0.69	$ 0.66	$ (20.94)	$ 3.54	$ 1.55
Net income (loss) per common share - fully diluted	$ (20.91)	$ (0.02)	$ (0.16)	$ 0.16	$ 1.36	$ 0.81	$ 0.68	$ 0.66	$ (20.94)	$ 3.51	$ 1.54