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Stock-Based Compensation and Employee Benefit Plans - Fair Value of Employee Stock Purchase Rights (Detail) (Employee Stock Purchase Rights [Member], USD $)
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9 Months Ended | |
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Sep. 30, 2012
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Sep. 30, 2011
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Employee Stock Purchase Rights [Member]
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Weighted-average grant date fair value per share | $ 1.28 | $ 2.46 |
| Risk-free interest rate | 0.15% | 0.07% |
| Dividend yield | ||
| Expected life (years) | 6 months | 6 months |
| Volatility | 46.60% | 45.70% |