Financial Instruments and Risk Management (Derivative Instruments, Fair Value) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Noncurrent assets	$ 5,439,000		$ 40,577,000
Noncurrent liabilities	(398,000)		(11,305,000)
Expected change in fair value of open Level 3 derivative contracts	19,000,000
Resulting impact upon the results of operations associated with open Level 3 mark-to-market derivative contracts	19,000,000
Fair Value, Measurements, Recurring
Derivative [Line Items]
Current assets	17,463,000		64,792,000
Noncurrent assets	5,439,000		40,577,000
Current liabilities	(30,302,000)		(2,593,000)
Noncurrent liabilities			(9,600,000)
Net derivative asset	(7,400,000)		93,176,000
Level 2 | Fair Value, Measurements, Recurring
Derivative [Line Items]
Current assets	(1,658,000)	[1]	(3,629,000)	[1]
Noncurrent assets	4,383,000	[1]	18,899,000	[1]
Current liabilities	(28,414,000)	[1]	(2,593,000)	[1]
Noncurrent liabilities			(8,520,000)	[1]
Net derivative asset	(25,689,000)	[1]	4,157,000	[1]
Level 3 | Fair Value, Measurements, Recurring
Derivative [Line Items]
Current assets	19,121,000	[1]	68,421,000	[1]
Noncurrent assets	1,056,000	[1]	21,678,000	[1]
Current liabilities	(1,888,000)	[1]	0	[1]
Noncurrent liabilities			(1,080,000)	[1]
Net derivative asset	18,289,000	[1]	89,019,000	[1]
Alabama Gas Corporation | Level 2 | Fair Value, Measurements, Recurring
Derivative [Line Items]
Current liabilities	$ 0		$ (2,600,000)

[1] Amounts classified in accordance with accounting guidance which permits offsetting fair value amounts recognized for multiple derivative instruments executed with the same counterparty under a master netting arrangement.