Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2011	Feb. 15, 2012	Jun. 30, 2011
Entity Information
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Entity Registrant Name	ENERGEN CORP
Entity Central Index Key	0000277595
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		72,107,881
Entity Current Reporting Status	Yes
Entity Voluntary Filer	No
Entity Well Known Seasoned Issuer	Yes
Entity Public Float			$ 4,036,291,000
Alabama Gas Corporation
Entity Information
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Entity Registrant Name	ALABAMA GAS CORP
Entity Central Index Key	0000003146
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		1,972,052