Organization and Basis of Presentation - Discontinued Operations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations	$ 436,620	$ (24,705)	$ 469,490	$ 24,213
Income (Loss) From Discontinued Operations	(3,485)	(9,027)	30,435	39,891
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Alagasco net income (loss)	(1,767)	(8,961)	40,646	37,557
Depreciation, depletion and amortization	(103)	(150)	(408)	(443)
General and administrative	1,710	1,158	3,337	4,784
Interest expense	(4,329)	(3,676)	(17,306)	(9,786)
Other income	0	(409)	(347)	(882)
Income tax expense	1,029	1,145	5,567	2,392
Income (Loss) From Discontinued Operations	(3,460)	(10,893)	31,489	33,622
Parent Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations	$ (25)	$ 1,866	$ (1,054)	$ 6,269