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Per Share Information - Additional Information (Detail)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2012
Exchangeable Shares [Member]
Dec. 31, 2011
Exchangeable Shares [Member]
Oct. 25, 2010
Exchangeable Shares [Member]
Dec. 31, 2010
Convertible Subordinated Debt [Member]
Earnings Per Share [Line Items]            
Interest rate of convertible subordinated notes           3.75%
Common stock, shares issued 220,917,050 217,479,462 3,909,110 3,909,110 3,909,110