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Assumptions Used to Estimate Fair Value of SARs Granted (Detail) (USD $)
9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Stock Appreciation Rights (SARs)
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield      
Risk-free interest rate 1.37% 0.78%
Volatility 91.00% 86.90%
Expected term (years) 5 years 5 years
Weighted average fair value of SARs granted $ 1.08 $ 1.26
Stock Options Granted
   
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Dividend yield     
Risk-free interest rate 0.78%  
Volatility 73.60%  
Expected term (years) 3 years 10 months 24 days  
Weighted average fair value of SARs granted $ 0.84