Quarterly Financial Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013 MMcfe	Dec. 31, 2012 MMcfe
Selected Quarterly Financial Information [Abstract]
Total operating revenues	$ 1,481,823	$ 762,490	$ 311,338	$ 164,981	$ 480,014	$ 384,522	$ 387,144	$ 61,454	$ 2,720,632	$ 1,313,134	$ 735,718
Total operating expenses	454,106	381,091	316,641	269,060	561,332	161,914	138,758	109,923	1,420,898	971,927	291,703
Operating income (loss)	1,027,717	381,399	(5,303)	(104,079)	(81,318)	222,608	248,386	(48,469)	1,299,734	341,207	444,015
Income (loss) from continuing operations	608,970	203,909	(44,495)	(94,759)	(225,177)	117,794	131,193	(47,997)
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest									673,625	(24,187)	225,276
Income (loss) from discontinued operations			2,210		2,157	3,100			2,210	5,257	(510,345)
Net income (loss) including noncontrolling interest	608,970	203,909	(42,285)	(94,759)					675,835	(18,930)	(285,069)
Net Income (Loss) Attributable to Noncontrolling Interest	2,248								2,248
Net income (loss)	$ 606,722	$ 203,909	$ (42,285)	$ (94,759)	$ (223,020)	$ 120,894	$ 131,193	$ (47,997)	$ 675,835	$ (18,930)	$ (285,069)
Earnings (loss) per common share - basic:
Continuing operations - basic	$ 2.31	$ 0.78	$ (0.17)	$ (0.36)	$ (0.86)	$ 0.45	$ 0.50	$ (0.18)	$ 2.56	$ (0.09)	$ 0.86
Discontinued operations - basic			$ 0.01		$ 0.01	$ 0.01			$ 0.01	$ 0.02	$ (1.95)
Net income (loss) - basic	$ 2.31	$ 0.78	$ (0.16)	$ (0.36)	$ (0.85)	$ 0.46	$ 0.50	$ (0.18)	$ 2.57	$ (0.07)	$ (1.09)
Earnings (loss) per share - diluted:
Continuing operations - diluted	$ 2.31	$ 0.78	$ (0.17)	$ (0.36)	$ (0.86)	$ 0.45	$ 0.50	$ (0.18)	$ 2.56	$ (0.09)	$ 0.86
Discontinued operations - diluted			$ 0.01		$ 0.01	$ 0.01			$ 0.01	$ 0.02	$ (1.95)
Net income (loss) - diluted	$ 2.31	$ 0.78	$ (0.16)	$ (0.36)	$ (0.85)	$ 0.46	$ 0.50	$ (0.18)	$ 2.57	$ (0.07)	$ (1.09)
Reduction of proved reserves resulted from downward price revisions										788,000	102,000