Discontinued Operations Balance Sheet and Income Statement (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash					$ 3,032,000
Accounts receivable					107,849,000
Inventories					41,268,000
Oil and gas properties					348,379,000
Less accumulated depreciation, depletion and amortization					(301,609,000)
Utility plant					1,491,433,000
Less accumulated depreciation					(605,924,000)
Other property, net					206,000
Other current assets					29,458,000
Other long-term assets					128,780,000
Total assets held for sale					1,242,872,000
Total assets held for sale
Accounts payable					(50,396,000)
Royalty payable					(1,419,000)
Accrued taxes					(28,027,000)
Notes payable to banks					(50,000,000)
Other current liabilities					(105,413,000)
Other long-term liabilities					(346,392,000)
Long-term debt					(249,923,000)
Total liabilities held for sale					(831,570,000)
Total net assets held for sale					411,302,000
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Natural gas distribution revenues	39,874,000	48,368,000	397,648,000	390,567,000
Oil and natural gas revenues	6,000	18,258,000	5,217,000	55,483,000
Total revenues	39,880,000	66,626,000	402,865,000	446,050,000
Pretax income (loss) from discontinued operations	(5,938,000)	(14,677,000)	48,581,000	64,098,000
Income tax expense (benefit)	(2,453,000)	(5,650,000)	18,146,000	24,207,000
Income (Loss) From Discontinued Operations	(3,485,000)	(9,027,000)	30,435,000	39,891,000
Gain (loss) on disposal of discontinued operations	726,410,000	(24,612,000)	724,743,000	(24,612,000)
Income tax expense (benefit)	286,305,000	(8,934,000)	285,688,000	(8,934,000)
Gain (Loss) on Disposal of Discontinued Operations	440,105,000	(15,678,000)	439,055,000	(15,678,000)
Income (Loss) From Discontinued Operations	436,620,000	(24,705,000)	469,490,000	24,213,000
Diluted Earnings Per Average Common Share
Income (Loss) from Discontinued Operations (in dollars per share)	$ (0.05)	$ (0.12)	$ 0.42	$ 0.55
Loss on Disposal of Discontinued Operations (in dollars per share)	$ 5.99	$ (0.22)	$ 5.99	$ (0.21)
Total Income (Loss) From Discontinued Operations (in dollars per share)	$ 5.94	$ (0.34)	$ 6.41	$ 0.34
Basic Earnings Per Average Common Share
Income (Loss) from Discontinued Operations (in dollars per share)	$ (0.05)	$ (0.12)	$ 0.42	$ 0.55
Loss on Disposal of Discontinued Operations (in dollars per share)	$ 6.03	$ (0.22)	$ 6.03	$ (0.21)
Total Income (Loss) From Discontinued Operations (in dollars per share)	$ 5.98	$ (0.34)	$ 6.45	$ 0.34
Adjustment for affiliated companies receivables					4,700,000
Reclassification from accrued taxes to other current assets					1,600,000
Reclassification from accrued taxes to other current liabilities					500,000
Alabama Gas Corporation
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash					3,032,000
Accounts receivable					103,748,000
Inventories					41,200,000
Oil and gas properties					0
Less accumulated depreciation, depletion and amortization					0
Utility plant					1,491,433,000
Less accumulated depreciation					(605,924,000)
Other property, net					41,000
Other current assets					29,458,000
Other long-term assets					128,780,000
Total assets held for sale					1,191,768,000
Total assets held for sale
Accounts payable					(48,653,000)
Royalty payable					0
Accrued taxes					(28,027,000)
Notes payable to banks					(50,000,000)
Other current liabilities					(105,013,000)
Other long-term liabilities					(331,409,000)
Long-term debt					(249,923,000)
Total liabilities held for sale					(813,025,000)
Total net assets held for sale					378,743,000
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Income (Loss) From Discontinued Operations	(3,460,000)	(10,893,000)	31,489,000	33,622,000
Black Warrior Basin
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash					0
Accounts receivable					2,829,000
Inventories					0
Oil and gas properties					0
Less accumulated depreciation, depletion and amortization
Utility plant					0
Less accumulated depreciation					0
Other property, net					0
Other current assets					0
Other long-term assets					0
Total assets held for sale					2,829,000
Total assets held for sale
Accounts payable					(1,732,000)
Royalty payable					(550,000)
Accrued taxes					0
Notes payable to banks					0
Other current liabilities					(379,000)
Other long-term liabilities					0
Long-term debt					0
Total liabilities held for sale					(2,661,000)
Total net assets held for sale					168,000
North Louisiana/East Texas
Assets of Disposal Group, Including Discontinued Operation [Abstract]
Cash					0
Accounts receivable					1,272,000
Inventories					68,000
Oil and gas properties					348,379,000
Less accumulated depreciation, depletion and amortization					(301,609,000)
Utility plant					0
Less accumulated depreciation					0
Other property, net					165,000
Other current assets					0
Other long-term assets					0
Total assets held for sale					48,275,000
Total assets held for sale
Accounts payable					(11,000)
Royalty payable					(869,000)
Accrued taxes					0
Notes payable to banks					0
Other current liabilities					(21,000)
Other long-term liabilities					(14,983,000)
Long-term debt					0
Total liabilities held for sale					(15,884,000)
Total net assets held for sale					$ 32,391,000