Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Cost Incurred in Oil and Gas Property Acquisition Exploration and Development Activities (Details)

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Supplemental Oil and Gas Disclosures - Cost Incurred in Oil and Gas Property Acquisition Exploration and Development Activities (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Costs incurred:      
Proved properties acquisitions [1] $ 1.3 $ 15.6 $ 111.5
Exploration [1],[2],[3] 4.8 152.4 411.1
Development [1] 56.9 65.5 198.7
Unproved property acquisitions [1],[4] 0.5 0.1 3.1
Total costs incurred in oil and gas property acquisition, exploration and development activities [1] $ 63.5 $ 233.6 $ 724.4
[1] Includes net addition from capitalized ARO of $10.8 million in 2016, net reductions from capitalized ARO of $0.4 million in 2015, and net additions from capitalized ARO of $88.0 million during 2014. These adjustments for ARO are associated with acquisitions, liabilities incurred, divestitures and revisions of estimates.
[2] Includes geological and geophysical costs charged to expense of $4.1 million, $5.7 million and $7.3 million during 2016, 2015 and 2014, respectively.
[3] Includes seismic costs of $0.2 million, $3.2 million and $9.0 million incurred during 2016, 2015 and 2014, respectively.
[4] The amounts for unproved property acquisitions include capitalized interest associated with unproved properties acquired during the period.