Commitments and Contingencies (Lease Obligations) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating Leased Assets [Line Items]
Total lease payments	$ 20,900,000	$ 19,100,000	$ 18,600,000
Operating Leases, Future Minimum Payments Due [Abstract]
2013	5,144,000
2014	4,836,000
2015	4,506,000
2016	4,141,000
2017	3,980,000
2018 and thereafter	13,046,000
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2013	1,743,000
2014	1,743,000
2015	145,000
Total minimum lease payments	3,631,000
Less amount representing interest	54,000
Total present value of minimum lease payments	3,577,000
Alabama Gas Corporation
Operating Leased Assets [Line Items]
Leasing term	25 years
Total lease payments	2,100,000	2,300,000	2,100,000
Lease expense paid by parent company	1,000,000
Operating Leases, Future Minimum Payments Due [Abstract]
2013	3,629,000
2014	3,858,000
2015	3,909,000
2016	3,934,000
2017	3,980,000
2018 and thereafter	13,046,000
Alabama Gas Corporation | Company's headquarters
Operating Leased Assets [Line Items]
Payments associated with leasing of Company's headquarters	$ 17,600,000