Organization and Basis of Presentation - Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations	$ 0	$ 37,669
Income From Discontinued Operations		38,719
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Alagasco net income		43,028
Depreciation, depletion and amortization		(152)
General and administrative		940
Interest expense		(5,787)
Other income		(119)
Income tax expense		1,935
Income From Discontinued Operations		39,845
Parent Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations		$ (1,126)