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Fair Value of Financial Instruments and Investments - Additional Information (Detail) (USD $)
9 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Fair Value of Financial Instruments [Line Items]    
Notes, outstanding $ 293,382,000 $ 293,382,000
Notes, carrying value 135,658,000 125,827,000
Convertible notes due 2018, interest rate 4.75%  
Notes, carrying value 100,073,000 97,087,000
Senior Notes Due 2019
   
Fair Value of Financial Instruments [Line Items]    
Notes, outstanding 170,900,000  
Notes, carrying value 135,700,000  
Senior Convertible Notes Due 2018
   
Fair Value of Financial Instruments [Line Items]    
Notes, outstanding 122,400,000  
Convertible notes due 2018, interest rate 4.75%  
Notes, carrying value 100,100,000  
Senior Convertible Notes Due 2018 | Level 1
   
Fair Value of Financial Instruments [Line Items]    
Notes, fair value $ 29,400,000  
Certificates of deposit | Maximum
   
Fair Value of Financial Instruments [Line Items]    
Short-term investment in certificates of deposits, maturity term 1 year 1 year