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Per Share Information (Narrative) (Detail)
Sep. 30, 2012
Dec. 31, 2011
Oct. 25, 2010
Class of Stock [Line Items]      
Common stock, shares issued 220,820,903 217,479,462  
Exchangeable Shares [Member]
     
Class of Stock [Line Items]      
Common stock, shares issued 3,909,110 3,909,110 3,900,000