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Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | $ 3,112 | $ 2,880 | $ 8,830 | $ 7,629
Research and Development Expense |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 761 | 667 | 1,972 | 1,520
Research and Development Expense | Stock Options |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 403 | 259 | 987 | 732
Research and Development Expense | Restricted Stock Units |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 210 | 190 | 617 | 493
Research and Development Expense | ESPP |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 148 | 218 | 368 | 295
General and Administrative Expense |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 2,351 | 2,213 | 6,858 | 6,109
General and Administrative Expense | Stock Options |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 1,799 | 1,766 | 5,257 | 4,920
General and Administrative Expense | Restricted Stock Units |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 532 | 381 | 1,521 | 1,095
General and Administrative Expense | ESPP |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | $ 20 | $ 66 | $ 80 | $ 94

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