Commitments and Contingencies - Commitments and Agreements (Details) (USD $) In Millions, unless otherwise specified	2 Months Ended	12 Months Ended					3 Months Ended
	Jan. 15, 2012 agreement	Dec. 31, 2012 Cadenhead Well MBoe	Mar. 31, 2013 Cadenhead Well MBoe	Mar. 31, 2013 Contract Termination	Mar. 31, 2013 Alabama Gas Corporation site	Mar. 31, 2013 Crude Oil and Natural Gas MBoe	Mar. 31, 2013 Natural Gas, Delivery and Storage Alabama Gas Corporation	Mar. 31, 2012 Natural Gas, Delivery and Storage Alabama Gas Corporation	Mar. 31, 2013 Natural Gas Alabama Gas Corporation Mcf	Mar. 31, 2013 Wholly Owned Properties Alabama Gas Corporation site
Long-term Purchase Commitment [Line Items]
Remaining contractual volume						29,600
Number of agreements to secure drilling rigs	3
Maximum loss contingency range of possible loss				$ 19
Long-term purchase commitment							94
Long-term purchase commitment, time period							September 2024		August 2020
Long-term commitments expense recognized in statement of operations							14.4	14.3
Long-term purchase commitment minimum quantity required									158,000,000
Recorded unconditional purchase obligation, time period									January 2014
Recorded unconditional purchase obligation									1.1
Recorded unconditional purchase obligation, market value									$ 1.2
Working interest			50.00%
Production (BOE)		63
Expected production (BOE)			34
Chain of title, manufactured gas plant sites					9					4
Chain of title, manufactured gas distribution sites					5					1