Summarized Quarterly Financial Data (Unaudited) (Quarterly Operating Results) (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		$ 192,799	$ 295,571	$ 168,326	$ 221,858					$ 878,554	$ 1,679,213	$ 1,206,293
Discontinued operations											402,847	593,529
Reclassification of loss on sale of assets and other										(26,570)	2,642	981
Operating income (loss)		(915,550)	(348,214)	(161,678)	(12,409)					(1,437,851)	176,961	252,137
Income (loss) from continuing operations		(590,806)	(227,904)	(111,601)	(15,420)	$ 66,519	$ 20,631	$ (3,154)	$ 15,647	(945,731)	99,643	141,881
Net income (loss)		$ (590,806)	$ (227,904)	$ (111,601)	$ (15,420)	$ 65,418	$ 457,251	$ (7,953)	$ 53,316	$ (945,731)	$ 568,032	$ 204,554
Diluted earnings per average common share
Continuing operations (in dollars per share)		$ (7.50)	$ (2.89)	$ (1.52)	$ (0.21)	$ 0.91	$ 0.28	$ (0.04)	$ 0.21	$ (12.43)	$ 1.36	$ 1.96
Net income (loss) (in dollars per share)		(7.50)	(2.89)	(1.52)	(0.21)	0.89	6.22	(0.11)	0.73	(12.43)	7.75	2.82
Basic earnings per average common share
Continuing operations (in dollars per share)		(7.50)	(2.89)	(1.52)	(0.21)	0.91	0.28	(0.04)	0.22	(12.43)	1.37	1.96
Net income (loss) (in dollars per share)		$ (7.50)	$ (2.89)	$ (1.52)	$ (0.21)	$ 0.90	$ 6.26	$ (0.11)	$ 0.73	$ (12.43)	$ 7.79	$ 2.83
Originally reported
Selected Quarterly Financial Information [Abstract]
Revenues						$ 611,435	$ 497,761	$ 270,097	$ 561,178
Operating income (loss)						94,223	48,171	3,107	104,599
Adjustment
Selected Quarterly Financial Information [Abstract]
Revenues						612,268	498,508	271,006	297,431
Discontinued operations	[1]					0	0	0	(263,900)
Reclassification of loss on sale of assets and other						833	747	909	153
Operating income (loss)						94,223	48,171	3,107	31,460
Discontinued operations	[1]					$ 0	$ 0	$ 0	$ (73,139)

[1] As discussed in Note 16, Discontinued Operations and Held for Sale Properties, during the third quarter of 2014, Energen completed the transaction to sell Alagasco to Laclede. During the second quarter of 2014, Energen classified Alagasco as held for sale and reflected the associated operating results in discontinued operations.