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Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) (USD $)
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3 Months Ended | |
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Mar. 31, 2013
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Mar. 31, 2012
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Employee Stock Options [Member]
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| Weighted-average fair value valuation assumptions | ||
| Risk-free interest rate | 1.15% | 1.16% |
| Expected term (in years) | 6 years 7 days | 6 years 29 days |
| Dividend yield | ||
| Volatility | 101.00% | 105.00% |
| Weighted-average fair value of stock options granted | $ 4.01 | $ 2.52 |
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Employee Stock Purchase Plan (ESPP) [Member]
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| Weighted-average fair value valuation assumptions | ||
| Risk-free interest rate | 0.20% | 0.20% |
| Expected term (in years) | 1 year 3 months | 1 year 3 months |
| Dividend yield | ||
| Volatility | 92.00% | 111.00% |
| Weighted-average fair value of stock options granted | $ 2.44 | $ 2.04 |
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- Details
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- Definition
The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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