Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance of ARO, beginning	$ 118,023		$ 107,340	$ 97,415
Liabilities incurred	2,772		3,994	4,627
Liabilities settled	(5,525)		(845)	(1,539)
Accretion expense	8,192		7,534	6,837
Reclassification associated with held for sale properties	(14,929)	[1]
Balance of ARO, end	108,533		118,023	107,340
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets, Noncurrent	84,890		110,566
Accretion expense from discontinued operations	1,197		1,195	1,138
Alabama Gas Corporation
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance of ARO, end	27,500		24,900
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets, Noncurrent	84,890		110,566
Alabama Gas Corporation | Asset removal costs
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets, Noncurrent	$ 4,601		$ 3,322

[1] Asset retirement obligation associated with North Louisiana/East Texas properties are included as liabilities related to assets held for sale in current liabilities on the balance sheet.