Acquisition and Dispositions of Properties (Details) (USD $)	3 Months Ended		12 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Alabama Gas Corporation	Mar. 31, 2013 Alabama Gas Corporation	Aug. 31, 2013 Birmingham Metro Operations Center Alabama Gas Corporation	Mar. 31, 2014 Birmingham Metro Operations Center Alabama Gas Corporation
Gas and Oil Acreage [Line Items]
Gain on disposition of property, plant and equipment				$ 612,000	$ 0	$ 10,900,000
Sales price							13,800,000
Lease back period after sale							20 months
Acquisitions, net of cash acquired	$ 6,537,000	$ 13,146,000	$ 31,300,000