Summary of Significant Accounting Policies (Discontinued Operations) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations	$ 468,389	$ 62,673	$ 48,941
Income from discontinued operations	29,292	59,079	48,941
Alabama Gas Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Alagasco net income	40,646	57,399	49,402
Depreciation, depletion and amortization	(408)	(598)	(572)
General and administrative	3,337	5,894	5,166
Interest expense	(17,306)	(13,815)	(1,693)
Other income	(347)	(1,342)	(977)
Income tax expense (benefit)	5,567	3,728	(727)
Income From Discontinued Operations	31,489	51,266	50,599
Parent Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income From Discontinued Operations	$ (2,197)	$ 7,813	$ (1,658)