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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 | 6 Months Ended | ||
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Jun. 30, 2014
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Jun. 30, 2013
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Jun. 30, 2014
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Jun. 30, 2013
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total stock-based compensation | $ 1,016 | $ 855 | $ 2,016 | $ 1,603 |
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Research and development [Member]
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total stock-based compensation | 495 | 415 | 942 | 727 |
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General and administrative [Member]
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| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total stock-based compensation | $ 521 | $ 440 | $ 1,074 | $ 876 |