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Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Oct. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares) | 7,258,353 | 6,706,994 |  |
Weighted average exercise price (in dollars per share) | $ 21.48 | $ 22.33 |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |
Stock-based compensation expense | $ 20,676 | $ 19,571 | $ 16,520 |
Equity Incentive Plan 2003 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares) | 249,959 |  |  |
Weighted average exercise price (in dollars per share) | $ 2.79 |  |  |
Stock Incentive Plan 2013 |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Share-based compensation, number of shares authorized (in shares) |  |  |  | 1,960,168
Increased number of shares authorized (in shares) | 11,896,613 |  |  |
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares) | 7,008,394 |  |  |
Weighted average exercise price (in dollars per share) | $ 22.14 |  |  |
Minimum annual increase (in shares) | 1,960,168 |  |  |
Percentage of common stock share outstanding | 4.00% |  |  |
Research and development |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |
Stock-based compensation expense | $ 10,833 | 10,023 | 7,919 |
General and administrative |  |  |  |
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] |  |  |  |
Stock-based compensation expense | $ 9,843 | $ 9,548 | $ 8,601 |

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