Stock-based Compensation - Schedule of Total Stock-based Compensation Expense Recognized in Connection with All Share-based Payment Awards (Detail) (USD $)
In Thousands, unless otherwise specified |
12 Months Ended | ||
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Dec. 31, 2014
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Dec. 31, 2013
|
Dec. 31, 2012
|
|
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Total stock-based compensation expense | $ 14,240 | $ 3,785 | $ 653 |
Research and Development [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Total stock-based compensation expense | 7,078 | 2,567 | 605 |
General and Administrative [Member] | |||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | |||
Total stock-based compensation expense | $ 7,162 | $ 1,218 | $ 48 |