Long-Term Debt and Notes Payable - Narratives (Details) (USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				6 Months Ended					0 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Alabama Gas Corporation	Jun. 30, 2013 Alabama Gas Corporation	Jun. 30, 2014 Alabama Gas Corporation	Jun. 30, 2013 Alabama Gas Corporation	Jun. 30, 2014 Energen Corporation	Dec. 31, 2013 Energen Corporation Senior Loans Senior Term Loans due March 31, 2014 to December 17, 2017	Jun. 30, 2014 Minimum	Jun. 30, 2014 Minimum Alabama Gas Corporation	Jun. 30, 2014 Maximum	Jun. 30, 2014 Maximum Alabama Gas Corporation	Oct. 30, 2012 Syndicated Credit Facility Alabama Gas Corporation	Oct. 30, 2012 Syndicated Credit Facility Energen Corporation	Jun. 30, 2014 Syndicated Credit Facility Energen Corporation	Jun. 30, 2014 APSC Authorized Short-term Line of Credit Alabama Gas Corporation
Debt Instrument [Line Items]
Long term debt										$ 600,000,000
Cross default provision, threshold amount					10,000,000		10,000,000		10,000,000
Maximum borrowing capacity	100,000,000		100,000,000												100,000,000	1,250,000,000.00
Debt instrument term																5 years	5 years
Authorized amount																		200,000,000
Maximum consolidated debt to capitalization ratio					65.00%		65.00%		65.00%
Credit facility cross default provision, threshold amount					50,000,000		50,000,000		50,000,000
Interest expense	7,964,000	10,182,000	15,852,000	20,083,000	3,745,000	3,833,000	7,710,000	7,863,000
Capitalized interest expense	$ 37,000	$ 34,000	$ 37,000	$ 200,000
Commitment fee percentage on the unused portion of available credit facilities											0.15%	0.15%	0.25%	0.25%