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Carrying Values of Convertible Senior Debentures (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Debt Instrument [Line Items]    
Convertible senior debentures-non-current $ 48,991 $ 45,694
Convertible Senior Debentures due 2018
   
Debt Instrument [Line Items]    
Convertible senior debentures 48,483  
Convertible Senior Debentures due 2014
   
Debt Instrument [Line Items]    
Convertible senior debentures 67 45,253
Convertible Senior Debentures due 2024
   
Debt Instrument [Line Items]    
Convertible senior debentures $ 441 $ 441