Annual report pursuant to Section 13 and 15(d)

Supplemental Oil And Gas Disclosures (Capitalized Costs Not Subject To Amortization) (Details)

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Supplemental Oil And Gas Disclosures (Capitalized Costs Not Subject To Amortization) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Dec. 31, 2008
Supplemental Oil And Gas Disclosures [Abstract]        
Acquisition costs $ 81.3     $ 44.4
Capitalized interest not subject to amortization 9.6 4.8 4.2 10.2
Total costs not subject to amortization 90.9 4.8 4.2 54.6
Acquisition costs, Total 125.7      
Capitalized interest not subject to amortization, Total 28.8      
Total costs not subject to amortization, Total $ 154.5