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Equity Incentive Plans - Fair Value of Each Stock Option Granted Weighted-Average Assumptions (Detail) (USD $)
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12 Months Ended | ||
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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| Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract] | |||
| Fair value of options granted | $ 1.69 | $ 1.26 | $ 1.33 |
| Expected volatility | 91.00% | 89.00% | 78.00% |
| Risk-free interest rate | 1.30% | 1.50% | 2.20% |
| Expected lives | 7 years | 7 years | 7 years |
| Dividend rate | |||