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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 | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | $ 3,011 | $ 2,463 | $ 5,718 | $ 4,749
Research and Development Expense |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 696 | 442 | 1,211 | 853
Research and Development Expense | Stock Options |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 340 | 246 | 584 | 474
Research and Development Expense | Restricted Stock Units |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 243 | 196 | 407 | 303
Research and Development Expense | ESPP |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 113 |  | 220 | 76
General and Administrative Expense |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 2,315 | 2,021 | 4,507 | 3,896
General and Administrative Expense | Stock Options |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 1,756 | 1,654 | 3,458 | 3,154
General and Administrative Expense | Restricted Stock Units |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | 528 | $ 367 | 989 | 714
General and Administrative Expense | ESPP |  |  |  |
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items] |  |  |  |
Total stock-based compensation expense | $ 31 |  | $ 60 | $ 28

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