Acquisition and Dispositions of Properties	3 Months Ended
Mar. 31, 2013
Extractive Industries [Abstract]
Acquisition and Dispositions of Properties	ACQUISITION AND DISPOSITION OF PROPERTIES During the first quarter of 2013, Alagasco entered into a purchase and sale agreement to sell its Birmingham Metro Operations Center which is located on 11.7 acres in downtown Birmingham and has been in service since the 1940's. The sales price is approximately $14 million and the sale is expected to close in August of 2013. Effective upon closing, Alagasco plans to lease the facility from the purchaser for a period of approximately 18 months. During the first quarter of 2012, Energen Resources recognized a noncash impairment writedown on certain properties in East Texas of $21.5 million pre-tax to adjust the carrying amount of these properties to their fair value based on expected future discounted cash flows. Significant assumptions in valuing the proved reserves included the reserve quantities, anticipated operating costs, anticipated production taxes, future expected natural gas prices and basis differentials, anticipated production declines, and a discount rate of 10 percent commensurate with the risk of the underlying cash flow estimates. The impairment was caused by the impact of lower future natural gas prices. During the first quarter of 2012, future natural gas price curves shifted significantly lower, especially in the next 5 years. This nonrecurring impairment writedown is classified as Level 3 fair value.

ACQUISITION AND DISPOSITION OF PROPERTIES

During the first quarter of 2013, Alagasco entered into a purchase and sale agreement to sell its Birmingham Metro Operations Center which is located on 11.7 acres in downtown Birmingham and has been in service since the 1940's. The sales price is approximately $14 million and the sale is expected to close in August of 2013. Effective upon closing, Alagasco plans to lease the facility from the purchaser for a period of approximately 18 months.

During the first quarter of 2012, Energen Resources recognized a noncash impairment writedown on certain properties in East Texas of $21.5 million pre-tax to adjust the carrying amount of these properties to their fair value based on expected future discounted cash flows. Significant assumptions in valuing the proved reserves included the reserve quantities, anticipated operating costs, anticipated production taxes, future expected natural gas prices and basis differentials, anticipated production declines, and a discount rate of 10 percent commensurate with the risk of the underlying cash flow estimates. The impairment was caused by the impact of lower future natural gas prices. During the first quarter of 2012, future natural gas price curves shifted significantly lower, especially in the next 5 years. This nonrecurring impairment writedown is classified as Level 3 fair value.