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, 2013	Dec. 31, 2012	Dec. 31, 2013 Minimum	Dec. 31, 2013 Maximum	Dec. 31, 2013 Energen Corporation	Dec. 31, 2012 Energen Corporation	Oct. 30, 2012 Energen Corporation Syndicated Credit Facility	Dec. 31, 2013 Alabama Gas Corporation	Dec. 31, 2012 Alabama Gas Corporation	Dec. 31, 2013 Alabama Gas Corporation Minimum	Dec. 31, 2013 Alabama Gas Corporation Maximum	Dec. 31, 2013 Alabama Gas Corporation APSC Authorized Short-term Line of Credit	Oct. 30, 2012 Alabama Gas Corporation Syndicated Credit Facility
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	1,350,000,000	1,350,000,000					1,250,000,000						100,000,000
Debt Instrument, Term							5 years						5 years
Short-term line of credit, authorization to borrow												200,000,000
Notes payable to banks	539,000,000	643,000,000			489,000,000	566,000,000		50,000,000	77,000,000
Available for borrowings	811,000,000	707,000,000
Maximum amount outstanding at any month-end					901,000,000	643,000,000		75,000,000	77,000,000
Average daily amount outstanding					$ 804,895,000	$ 331,068,000		$ 35,027,000	$ 21,254,000
Average daily amount outstanding, weighted average interest rates					1.38%	1.82%		1.12%	1.44%
Amount outstanding at year-end, weighted average interest rates					1.32%	1.35%		1.26%	1.11%
Unused capacity, commitment fee percentage			1500.00%	2500.00%						1500.00%	2500.00%