Long-Term Debt and Notes Payable (Lines of Credit) (Details) (USD $)						12 Months Ended		0 Months Ended				12 Months Ended			0 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Syndicated Credit Facility [Member]	Dec. 31, 2011 Bryant Bank [Member]	Dec. 31, 2011 BancorpSouth Bank [Member]	Dec. 31, 2011 Energen Corporation	Dec. 31, 2010 Energen Corporation	Oct. 29, 2010 Energen Corporation Syndicated Credit Facility [Member]	Dec. 31, 2011 Energen Corporation Syndicated Credit Facility [Member]	Dec. 31, 2011 Energen Corporation Bryant Bank [Member]	Dec. 31, 2011 Energen Corporation BancorpSouth Bank [Member]	Dec. 31, 2011 Alabama Gas Corporation	Dec. 31, 2010 Alabama Gas Corporation	Dec. 31, 2011 Alabama Gas Corporation APSC Authorized Short-term Line of Credit	Oct. 29, 2010 Alabama Gas Corporation Syndicated Credit Facility [Member]	Dec. 31, 2011 Alabama Gas Corporation Syndicated Credit Facility [Member]	Dec. 31, 2011 Alabama Gas Corporation Bryant Bank [Member]	Dec. 31, 2011 Alabama Gas Corporation BancorpSouth Bank [Member]
Line of Credit Facility [Line Items]
Maximum consolidated debt to capitalization ratio	65.00%											65.00%
Cross default provision, minimum debt default amount	$ 50,000,000											$ 50,000,000
Line of Credit Facility [Abstract]
Credit facilities	1,019,000,000	1,019,000,000	1,000,000,000	9,000,000	10,000,000	850,000,000		850,000,000	850,000,000	0	0	169,000,000			150,000,000	150,000,000	9,000,000	10,000,000
Credit facilities term (in years)								3 years							3 years
Short-term line of credit, authorization to borrow														200,000,000
Notes payable to banks	15,000,000	305,000,000				0	235,000,000					15,000,000	70,000,000
Available for borrowings	1,004,000,000	714,000,000
Maximum amount outstanding at any month-end						363,000,000	305,000,000					70,000,000	70,000,000
Average daily amount outstanding						$ 229,094,000	$ 19,732,000					$ 29,268,000	$ 6,436,000
Average daily amount outstanding, weighted average interest rates						2.04%	2.07%					1.72%	1.56%
Amount outstnding at year-end, , weighted average interest rates						3.57%	2.03%					3.57%	1.90%