Quarterly report pursuant to Section 13 or 15(d)

Basis Of Presentation And Significant Accounting Policies (Narrative) (Detail)

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Basis Of Presentation And Significant Accounting Policies (Narrative) (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Related Party Transaction [Line Items]        
Change in net income(loss)   $ 30.4   $ 67.9
Noncontrolling interest   21.00%   21.00%
Renewafuel [Member]
       
Related Party Transaction [Line Items]        
Income (loss) from discontinued operations 0 (0.7) (0.1) (1.1)
Immaterial Errors [Member]
       
Related Party Transaction [Line Items]        
Change in income (loss) from continuing operations including portion attributable to noncontrolling interest   $ 7.7   $ 16.1
Change in earnings per share basic and diluted   $ 0.22   $ 0.49
Black Label And Black Thor Chromite Deposits [Member]
       
Related Party Transaction [Line Items]        
Ownership interest, percent 100.00%   100.00%  
Big Daddy Chromite Deposit [Member]
       
Related Party Transaction [Line Items]        
Ownership interest, percent 72.00%   72.00%