Long-Term Debt and Notes Payable - Credit Facilities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Energen Corporation
Line of Credit Facility [Line Items]
Notes payable to banks	$ 669,000	$ 489,000
Available for borrowings	581,000	761,000
Total Energen	1,250,000	1,250,000
Maximum amount outstanding at any month-end	669,000	901,000
Average daily amount outstanding	576,486	804,895
Average daily amount outstanding interest rate	1.42%	1.38%
Amount outstanding at period-end interest rate	1.40%	1.32%
Alabama Gas Corporation
Line of Credit Facility [Line Items]
Notes payable to banks	0	50,000
Available for borrowings	100,000	50,000
Total Energen	100,000	100,000
Maximum amount outstanding at any month-end	55,000	75,000
Average daily amount outstanding	$ 17,956	$ 35,027
Average daily amount outstanding interest rate	1.28%	1.12%
Amount outstanding at period-end interest rate	0.00%	1.26%