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Schedule of Weighted Average Stock Options Exercise Price (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award      
Outstanding at January 1 $ 4.12 $ 16.32 $ 13.87
Options granted $ 16.95 $ 16.23 $ 9.34
Assumed from acquisition   $ 2.69  
Options exercised $ 3.87 $ 4.38 $ 8.65
Options forfeited $ 3.11    
Options cancelled $ 16.21 $ 26.38 $ 19.54
Outstanding at December 31 $ 4.64 $ 4.12 $ 16.32
Exercisable at December 31 $ 3.70    
Stock Option
     
Share-based Compensation Arrangement by Share-based Payment Award      
Exercisable at December 31 $ 3.70 $ 4.10 $ 18.24