Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Outstanding Warrants Valuation Assumption (Detail)

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Stockholders' Equity - Outstanding Warrants Valuation Assumption (Detail) (USD $)
3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
August 2008 offering [Member]
   
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Risk-free interest rate 0.11% 0.16%
Expected life (in years) 4 months 28 days 7 months 28 days
Dividend yield      
Volatility 66.00% 118.00%
Stock price $ 4.61 $ 4.21
March 2011 offering [Member]
   
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Risk-free interest rate 0.36% 0.72%
Expected life (in years) 2 years 11 months 16 days 3 years 2 months 16 days
Dividend yield      
Volatility 95.00% 94.00%
Stock price $ 4.61 $ 4.21
October 2009 offering [Member]
   
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]    
Risk-free interest rate 0.25% 0.25%
Expected life (in years) 1 year 6 months 7 days 1 year 9 months 4 days
Dividend yield      
Volatility 103.00% 98.00%
Stock price $ 4.61 $ 4.21