Stock Based Compensation - Stock-Based Compensation Expense (Detail) (USD $)
In Thousands, unless otherwise specified |
3 Months Ended | |
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Mar. 31, 2014
|
Mar. 31, 2013
|
|
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||
Stock-based compensation expense | $ 1,266 | $ 1,053 |
Research and Development [Member]
|
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Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||
Stock-based compensation expense | 671 | 534 |
General and Administrative [Member]
|
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Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||
Stock-based compensation expense | $ 595 | $ 519 |