Employee Benefit Plans (Details) (USD $)	1 Months Ended	3 Months Ended
	Jan. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure
Number of defined benefit non-contributory pension plans and certain nonqualified supplemental pension plans		2
Pension Plans
Components of net periodic benefit cost:
Service cost		$ 3,003,000	$ 3,602,000
Interest cost		2,575,000	2,718,000
Expected long-term return on assets		(2,848,000)	(3,713,000)
Actuarial loss amortization		2,256,000	3,690,000
Prior service cost amortization		118,000	122,000
Settlement charge		7,262,000	144,000
Net periodic expense		12,366,000	6,563,000
Estimated required future employer contributions in current fiscal year		500,000
Contributions by employer in current fiscal year	3,000,000
Benefit payments made in current fiscal year		33,000
Estimated future benefit payments in current fiscal year		200,000
Settlement charges		17,100,000
Settlement charges expensed		6,900,000
Postretirement Benefit Plans
Components of net periodic benefit cost:
Service cost		170,000	444,000
Interest cost		754,000	869,000
Expected long-term return on assets		(1,412,000)	(1,242,000)
Actuarial loss amortization		(520,000)	0
Transition obligation amortization		27,000	324,000
Net periodic expense		(981,000)	395,000
Non-Qualified Supplemental Retirement Plans
Components of net periodic benefit cost:
Settlement charges		400,000	500,000
Settlement charges expensed			100,000
Alabama Gas Corporation | Pension Plans
Components of net periodic benefit cost:
Settlements recognized as a pension asset		10,200,000
Alabama Gas Corporation | Non-Qualified Supplemental Retirement Plans
Components of net periodic benefit cost:
Settlements recognized as a pension asset			$ 400,000