Commitments and Contingencies (Lease Obligations) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Leased Assets [Line Items]
Total lease payments	$ 25,000,000	$ 20,900,000	$ 19,100,000
Operating Leases, Future Minimum Payments Due [Abstract]
2014	5,270,000
2015	4,940,000
2016	4,391,000
2017	3,980,000
2018	2,409,000
2019 and thereafter	10,637,000
Alabama Gas Corporation
Operating Leased Assets [Line Items]
Total lease payments	2,400,000	2,100,000	2,300,000
Lease expense paid by parent company	700,000	1,000,000	1,000,000
Operating Leases, Future Minimum Payments Due [Abstract]
2014	4,291,000
2015	4,062,000
2016	3,994,000
2017	3,979,000
2018	2,409,000
2019 and thereafter	10,637,000
Alabama Gas Corporation | Company's headquarters
Operating Leased Assets [Line Items]
Leasing term	25 years
Payments associated with leasing of Company's headquarters	$ 16,200,000