Common Stock Plans (Energen Employee Savings Plan) (Details) (Energen Employee Savings Plan, USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Energen Employee Savings Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of common stock that might be diversified into other investment options	100.00%
Total shares reserved for issuance (in shares)	1,080,108
Expense associated with contributions to employee savings plan	$ 8.0	$ 7.8	$ 6.8