CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Premium on Capital Stock	Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Deferred Compensation Plan	Treasury Stock	Alabama Gas Corporation	Alabama Gas Corporation Common Stock	Alabama Gas Corporation Premium on Capital Stock	Alabama Gas Corporation Capital Surplus	Alabama Gas Corporation Retained Earnings
BALANCE at Dec. 31, 2010	$ 2,154,043	$ 748	$ 468,934	$ 2,802	$ 1,880,183	$ (74,397)	$ 3,288	$ (127,515)	$ 327,319	$ 20	$ 31,682	$ 2,802	$ 292,815
BALANCE, shares at Dec. 31, 2010		74,786,376								1,972,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	259,624				259,624				46,602				46,602
Other comprehensive income	44,145					44,145
Purchase of treasury shares, net	(713)							(713)
Shares issued for employee benefit plans, shares		221,036
Shares issued for employee benefit plans	7,237	2	7,235
Deferred compensation obligation	0						223	(223)
Stock-based compensation	5,763		5,763
Tax benefit from employee stock plans	986		986
Cash dividends, per share - ($0.54 in 2011, $0.56 in 2012, $0.58 in 2013)	(38,922)				(38,922)				(29,183)				(29,183)
BALANCE at Dec. 31, 2011	2,432,163	750	482,918	2,802	2,100,885	(30,252)	3,511	(128,451)	344,738	20	31,682	2,802	310,234
BALANCE, shares at Dec. 31, 2011		75,007,412								1,972,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	57,406								46,918
BALANCE at Mar. 31, 2012
BALANCE at Dec. 31, 2011	2,432,163	750	482,918	2,802	2,100,885	(30,252)	3,511	(128,451)	344,738	20	31,682	2,802	310,234
BALANCE, shares at Dec. 31, 2011		75,007,412								1,972,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	253,562				253,562				49,402				49,402
Other comprehensive income	21,941					21,941
Purchase of treasury shares, net	(277)							(277)
Shares issued for employee benefit plans, shares		60,348
Shares issued for employee benefit plans	2,061	1	2,060
Deferred compensation obligation	0						(737)	737
Stock-based compensation	7,082		6,580					502
Tax benefit from employee stock plans	550		550
Cash dividends, per share - ($0.54 in 2011, $0.56 in 2012, $0.58 in 2013)	(40,392)				(40,392)				(33,637)				(33,637)
BALANCE at Dec. 31, 2012	2,676,690	751	492,108	2,802	2,314,055	(8,311)	2,774	(127,489)	360,503	20	31,682	2,802	325,999
BALANCE, shares at Dec. 31, 2012	75,067,760	75,067,760							1,972,052	1,972,052
BALANCE at Sep. 30, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	62,823								12,197
BALANCE at Dec. 31, 2012	2,676,690			2,802					360,503	20	31,682	2,802
BALANCE, shares at Dec. 31, 2012	75,067,760								1,972,052	1,972,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	56,692								47,222
BALANCE at Mar. 31, 2013
BALANCE at Dec. 31, 2012	2,676,690	751	492,108	2,802	2,314,055	(8,311)	2,774	(127,489)	360,503	20	31,682	2,802	325,999
BALANCE, shares at Dec. 31, 2012	75,067,760	75,067,760							1,972,052	1,972,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	204,554				204,554				57,399				57,399
Other comprehensive income	(11,756)					(11,756)
Purchase of treasury shares, net	(1,038)							(1,038)
Shares issued for employee benefit plans, shares		506,396
Shares issued for employee benefit plans	18,795	5	18,790
Deferred compensation obligation	0						485	(485)
Stock-based compensation	9,625		6,869					2,756
Tax benefit from employee stock plans	3,142		3,142
Cash dividends, per share - ($0.54 in 2011, $0.56 in 2012, $0.58 in 2013)	(41,993)				(41,993)				(33,322)				(33,322)
BALANCE at Dec. 31, 2013	2,858,019	756	520,909	2,802	2,476,616	(20,067)	3,259	(126,256)	384,580	20	31,682	2,802	350,076
BALANCE, shares at Dec. 31, 2013	75,574,156	75,574,156							1,972,052	1,972,052
BALANCE at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	84,093								19,842
BALANCE at Dec. 31, 2013	$ 2,858,019			$ 2,802					$ 384,580	$ 20	$ 31,682	$ 2,802
BALANCE, shares at Dec. 31, 2013	75,574,156								1,972,052	1,972,052