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, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Supplemental Oil And Gas Disclosures [Abstract]      
Proved property acquisitions $ 369.9 [1] $ 277.3 [1] $ 17.5 [1]
Development 203.7 [1] 158.3 [1] 142.9 [1]
Exploration 92.7 [1],[2],[3] 70.8 [1],[2],[3] 101.6 [1],[2],[3]
Unproved property acquisitions 95.1 [1],[4] 19.7 [1],[4] 12.2 [1],[4]
Total costs incurred in oil and gas property acquisition, exploration and development activities 761.4 [1] 526.1 [1] 274.2 [1]
Additions (reductions) of asset retirement obligations 32.8 106.1 (6.0)
Seismic costs 8.0 5.8 6.6
Geological and geophysical costs $ 6.8 $ 4.3 $ 4.1
[1] Includes additions (reductions) to our ARO of $32.8 million, $106.1 million and ($6.0) million during the years 2011, 2010 and 2009, respectively, associated with acquisitions, liabilities incurred and revisions of estimates. Refer to Note 5.
[2] Includes seismic costs of $8.0 million, $5.8 million and $6.6 million incurred during the years 2011, 2010 and 2009, respectively.
[3] Includes geological and geophysical costs charged to expense of $6.8 million, $4.3 million and $4.1 million during the years 2011, 2010 and 2009, respectively.
[4] The amounts for 2011, 2010 and 2009 include capitalized interest associated with properties classified as unproved at December 31, 2011, 2010 and 2009, respectively.