Asset Retirement Obligations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Alabama Gas Corporation	Dec. 31, 2013 Alabama Gas Corporation	Jun. 30, 2014 Asset removal costs Alabama Gas Corporation	Dec. 31, 2013 Asset removal costs Alabama Gas Corporation
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of December 31, 2013			$ 108,533		$ 28,200	$ 27,500
Liabilities incurred			1,504
Liabilities settled			(676)
Accretion of discount on asset retirement obligations	1,883	1,729	3,726	3,416
Balance as of June 30, 2014	113,087		113,087		28,200	27,500
Regulatory assets, noncurrent					$ 91,857	$ 84,890	$ 3,405	$ 4,601