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Common Stock - Summary of Share-based Compensation Expense for Stock Options and Restricted Stock (Detail) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Share-based compensation | $ 887 | $ 581 | $ 2,490 | $ 1,610 |
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Research and development [Member]
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Share-based compensation | 410 | 243 | 1,137 | 671 |
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General and administrative [Member]
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Share-based compensation | $ 477 | $ 338 | $ 1,353 | $ 939 |