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Acquisition and Disposition of Properties	3 Months Ended
Acquisition and Disposition of Properties	Mar. 31, 2018
Business Combinations [Abstract]
Acquisition and Disposition of Properties	ACQUISITION AND DISPOSITION OF PROPERTIES In the first quarter of 2018, Energen completed acreage swaps which delivered 1,922.4 net acres in the Midland Basin to a third party, while it received 1,230.7 net acres in the Delaware Basin along with $0.7 million cash. Energen recognized a pre-tax gain of $33.4 million based on the fair value of the asset surrendered in the acreage trade. During the three months ended March 31, 2018, Energen completed an estimated total of $21.8 million in various purchases and renewals of unproved acquisitions, which are accounted for as asset acquisitions, including approximately $18.3 million in the Delaware Basin and approximately $3.5 million in the Midland Basin for unproved leasehold. During the three months ended March 31, 2017, Energen completed an estimated $157.8 million in various purchases and renewals of unproved acquisitions including approximately $111.9 million in the Delaware Basin and approximately $27.1 million in the Midland Basin for unproved leasehold and $18.8 million for mineral purchases in the Delaware Basin.