Supplemental Cash Flow Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Supplemental Cash Flow Information [Line Items]
Interest paid, net of amount capitalized	$ 31,023,000	$ 37,071,000	$ 37,032,000
Income taxes paid	9,432,000	83,894,000	48,061,000
Noncash investing activities:
Accrued development and exploration costs	72,030,000	75,167,000	46,107,000
Capitalized Depreciation	93,000	116,000	94,000
Capitalized asset retirement obligations costs	4,927,000	4,194,000	18,113,000
Allowance for funds used during construction	807,000	808,000	1,106,000
Issuance of common stock for employee benefit plans	822,000	5,765,000	641,000
Treasury stock acquired in connection with tax withholdings	713,000	2,894,000	778,000
Accretion expense	6,837,000	6,178,000	4,935,000
Treasury shares issued			300,000
Alabama Gas Corporation
Supplemental Cash Flow Information [Line Items]
Interest paid, net of amount capitalized	12,385,000	11,653,000	11,731,000
Income taxes paid	5,143,000	13,063,000	7,908,000
Interest paid on affiliated company debt, net	376,000	274,000	221,000
Noncash investing activities:
Accrued development and exploration costs	2,229,000	2,592,000	2,049,000
Capitalized Depreciation	93,000	116,000	94,000
Capitalized asset retirement obligations costs	300,000	161,000	229,000
Allowance for funds used during construction	$ 807,000	$ 808,000	$ 1,106,000