Long-Term Debt and Notes Payable - Long-Term Debt (Details) (USD $) In Thousands, unless otherwise specified																																			6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Energen Corporation	Dec. 31, 2013 Energen Corporation	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.40% Medium-term Notes, Series A, due July 24, 2017	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.40% Medium-term Notes, Series A, due July 24, 2017	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.36% Medium-term Notes, Series A, due July 24, 2017	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.36% Medium-term Notes, Series A, due July 24, 2017	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.23% Medium-term Notes, Series A, due July 28, 2017	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.23% Medium-term Notes, Series A, due July 28, 2017	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.32% Medium-term Notes, Series A, due July 28, 2022	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.32% Medium-term Notes, Series A, due July 28, 2022	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.60% Medium-term Notes, Series A, due July 26, 2027	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.60% Medium-term Notes, Series A, due July 26, 2027	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.35% Medium-term Notes, Series A, due July 28, 2027	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.35% Medium-term Notes, Series A, due July 28, 2027	Jun. 30, 2014 Energen Corporation Medium-term Notes 7.125% Medium-term Notes, Series B, due February 15, 2028	Dec. 31, 2013 Energen Corporation Medium-term Notes 7.125% Medium-term Notes, Series B, due February 15, 2028	Jun. 30, 2014 Energen Corporation Notes Payable 4.625% Notes, due September 1, 2021	Dec. 31, 2013 Energen Corporation Notes Payable 4.625% Notes, due September 1, 2021	Jun. 30, 2014 Energen Corporation Senior Term Loans Senior Term Loans, (floating rate interest LIBOR plus 1.625%; 1.775% at June 30, 2014), due September 30, 2014 to December 17, 2017	Dec. 31, 2013 Energen Corporation Senior Term Loans Senior Term Loans, (floating rate interest LIBOR plus 1.625%; 1.775% at June 30, 2014), due September 30, 2014 to December 17, 2017	Jun. 30, 2014 Alabama Gas Corporation	Dec. 31, 2013 Alabama Gas Corporation	Jun. 30, 2014 Alabama Gas Corporation Notes Payable 5.368% Notes, due December 1, 2015	Dec. 31, 2013 Alabama Gas Corporation Notes Payable 5.368% Notes, due December 1, 2015	Jun. 30, 2014 Alabama Gas Corporation Notes Payable 5.20% Notes, due January 15, 2020	Dec. 31, 2013 Alabama Gas Corporation Notes Payable 5.20% Notes, due January 15, 2020	Jun. 30, 2014 Alabama Gas Corporation Notes Payable 5.70% Notes, due January 15, 2035	Dec. 31, 2013 Alabama Gas Corporation Notes Payable 5.70% Notes, due January 15, 2035	Jun. 30, 2014 Alabama Gas Corporation Notes Payable 3.86% Notes, due December 21, 2021	Dec. 31, 2013 Alabama Gas Corporation Notes Payable 3.86% Notes, due December 21, 2021	Jun. 30, 2014 Alabama Gas Corporation Notes Payable 5.90% Notes, due January 15, 2037	Dec. 31, 2013 Alabama Gas Corporation Notes Payable 5.90% Notes, due January 15, 2037	Jun. 30, 2014 London Interbank Offered Rate (LIBOR) Energen Corporation Senior Term Loans Senior Term Loans, (floating rate interest LIBOR plus 1.625%; 1.775% at June 30, 2014), due September 30, 2014 to December 17, 2017
Debt Instrument [Line Items]
Gross amount			$ 1,124,000	$ 1,154,000	$ 2,000	$ 2,000	$ 15,000	$ 15,000	$ 2,000	$ 2,000	$ 20,000	$ 20,000	$ 5,000	$ 5,000	$ 10,000	$ 10,000	$ 100,000	$ 100,000	$ 400,000	$ 400,000	$ 570,000	$ 600,000	$ 249,830	$ 249,923	$ 80,000	$ 80,000	$ 40,000	$ 40,000	$ 34,830	$ 34,923	$ 50,000	$ 50,000	$ 45,000	$ 45,000
Less amounts due within one year	570,000	60,000	570,000	60,000																			50,000	0
Less unamortized debt discount			448	459
Long-term debt	$ 553,552	$ 1,093,541	$ 553,552	$ 1,093,541																			$ 199,830	$ 249,923
Interest Rate					7.40%		7.36%		7.23%		7.32%		7.60%		7.35%		7.125%		4.625%						5.368%		5.20%		5.70%		3.86%		5.90%
Floating rate interest spread																																			1.625%
Interest rate at period end																					1.775%