CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total		Common Stock	Premimum on Capital Stock [Member]	Capital Surplus [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Deferred Compensation Plan	Treasury Stock [Member]	Alabama Gas Corporation	Alabama Gas Corporation Common Stock	Alabama Gas Corporation Premimum on Capital Stock [Member]	Alabama Gas Corporation Capital Surplus [Member]	Alabama Gas Corporation Retained Earnings [Member]
BALANCE at Dec. 31, 2008	$ 1,913,290		$ 745	$ 454,778	$ 2,802	$ 1,405,970	$ 169,817	$ 2,948	$ (123,770)	$ 308,247	$ 20	$ 31,682	$ 2,802	$ 273,743
BALANCE, shares at Dec. 31, 2008			74,521,957								1,972,052
Net income	256,325					256,325				45,415				45,415
Other comprehensive income (loss):
Change in fair value of derivative instruments, net of tax of (($2,032) in 2009, $19,491 in 2010, $41,399 in 2011)	(3,316)						(3,316)
Reclassification adjustment, net of tax of (($90,799) in 2009, ($76,535) in 2010, ($8,953) in 2011)	(148,146)						(148,146)
Pension and postretirement plans, net of tax of (($397) in 2009, $570 in 2010, ($4,320) in 2011)	(740)						(740)
Comprehensive income	104,123
Purchase of treasury shares, net	(512)								(512)
Shares issued for employee benefit plans, shares			71,474
Shares issued for employee benefit plans	995		1	994
Deferred compensation obligation	0							173	(173)
Stock based compensation	5,283			5,283
Tax benefit from employee stock plans	606			606
Cash dividends, per share - ($0.50 in 2009, $0.52 in 2010, $0.54 in 2011)	(35,542)					(35,542)				(35,859)				(35,859)
BALANCE at Dec. 31, 2009	1,988,243		746	461,661	2,802	1,626,753	17,615	3,121	(124,455)	317,803	20	31,682	2,802	283,299
BALANCE, shares at Dec. 31, 2009			74,593,431								1,972,052
Net income	116,710									44,246
BALANCE at Mar. 31, 2010
BALANCE at Dec. 31, 2009	1,988,243		746	461,661	2,802	1,626,753	17,615	3,121	(124,455)	317,803	20	31,682	2,802	283,299
BALANCE, shares at Dec. 31, 2009			74,593,431								1,972,052
Net income	290,807					290,807				46,883				46,883
Other comprehensive income (loss):
Change in fair value of derivative instruments, net of tax of (($2,032) in 2009, $19,491 in 2010, $41,399 in 2011)	31,801						31,801
Reclassification adjustment, net of tax of (($90,799) in 2009, ($76,535) in 2010, ($8,953) in 2011)	(124,873)						(124,873)
Pension and postretirement plans, net of tax of (($397) in 2009, $570 in 2010, ($4,320) in 2011)	1,060						1,060
Comprehensive income	198,795
Purchase of treasury shares, net	(2,893)								(2,893)
Shares issued for employee benefit plans, shares			192,945
Shares issued for employee benefit plans	6,451		2	6,449
Deferred compensation obligation	0							167	(167)
Stock based compensation	(83)			(83)
Tax benefit from employee stock plans	907			907
Cash dividends, per share - ($0.50 in 2009, $0.52 in 2010, $0.54 in 2011)	(37,377)					(37,377)				(37,367)				(37,367)
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		74,786,376							1,972,052	1,972,052
BALANCE at Sep. 30, 2010
Net income	80,250									10,097
BALANCE at Dec. 31, 2010	2,154,043				2,802					327,319	20	31,682	2,802
BALANCE, shares at Dec. 31, 2010	74,786,376									1,972,052	1,972,052
Net income	94,268									44,175
BALANCE at Mar. 31, 2011
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		74,786,376							1,972,052	1,972,052
Net income	259,624					259,624				46,602				46,602
Other comprehensive income (loss):
Change in fair value of derivative instruments, net of tax of (($2,032) in 2009, $19,491 in 2010, $41,399 in 2011)	67,547						67,547
Reclassification adjustment, net of tax of (($90,799) in 2009, ($76,535) in 2010, ($8,953) in 2011)	(14,607)						(14,607)
Pension and postretirement plans, net of tax of (($397) in 2009, $570 in 2010, ($4,320) in 2011)	(7,854)						(7,854)
Interest rate swap, net of tax of (($507) in 2011)	(941)						(941)
Comprehensive income	303,769
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 - ($0.50 in 2009, $0.52 in 2010, $0.54 in 2011)	(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		75,007,412							1,972,052	1,972,052
BALANCE at Sep. 30, 2011
Net income	14,432	[1]								11,258
BALANCE at Dec. 31, 2011	$ 2,432,163				$ 2,802					$ 344,738	$ 20	$ 31,682	$ 2,802
BALANCE, shares at Dec. 31, 2011	75,007,412									1,972,052	1,972,052

[1] The three months ended December 31, 2011 includes an after-tax non-cash mark-to-market loss on derivatives of $56.6 million, or $0.78 per diluted share.