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Summary of Carrying Values and Estimated Fair Values of Senior Convertible Notes (Detail) (USD $)
Dec. 31, 2012
Dec. 31, 2011
Senior convertible notes due December 15, 2013
   
Financial Instruments [Line Items]    
Carrying value $ 114,443,000 $ 113,860,000
Estimated fair value 81,900,000 61,000,000
Senior convertible notes due August 15 2015
   
Financial Instruments [Line Items]    
Carrying value 97,583,000 96,782,000
Estimated fair value $ 63,200,000 $ 60,800,000