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Summary of Carrying Values and Estimated Fair Values of Senior Convertible Notes (Detail) (USD $)
Dec. 31, 2013
Dec. 31, 2012
Senior convertible notes due December 15, 2013
   
Convertible Debt [Line Items]    
Carrying value   $ 114,443,000
Estimated fair value   81,900,000
Senior convertible notes due August 15 2015
   
Convertible Debt [Line Items]    
Carrying value 98,439,000 97,583,000
Estimated fair value 102,200,000 63,200,000
Senior convertible notes due December 31 2019
   
Convertible Debt [Line Items]    
Carrying value 102,300,000  
Estimated fair value $ 107,000,000