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Stockholders' Equity - Outstanding Warrants Valuation Assumptions (Detail) (USD $)
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9 Months Ended | 12 Months Ended |
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Sep. 30, 2012
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Dec. 31, 2011
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August 2008 Offering [Member]
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] | ||
| Risk-free interest rate | 0.17% | 0.25% |
| Expected life (in years) | 10 months 28 days | 1 year 7 months 28 days |
| Dividend yield | ||
| Volatility | 118.00% | 84.00% |
| Exercise price | $ 1.86 | $ 1.86 |
| Stock price | $ 7.24 | $ 1.22 |
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October 2009 Offering [Member]
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] | ||
| Risk-free interest rate | 0.23% | 0.36% |
| Expected life (in years) | 2 years 4 days | 2 years 9 months 4 days |
| Dividend yield | ||
| Volatility | 105.00% | 88.00% |
| Exercise price | $ 2.05 | $ 2.05 |
| Stock price | $ 7.24 | $ 1.22 |
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March 2011 Offering [Member]
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| Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items] | ||
| Risk-free interest rate | 0.62% | 0.60% |
| Expected life (in years) | 3 years 5 months 16 days | 4 years 2 months 16 days |
| Dividend yield | ||
| Volatility | 99.00% | 102.00% |
| Exercise price | $ 2.46 | $ 2.46 |
| Stock price | $ 7.24 | $ 1.22 |