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Stock-Based Compensation - Stock options (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
May 03, 2019 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Share Based Compensation Expense Not Recognized |  |  |  |
Unrecognized compensation cost |  | $ 7,700,000 |  |
Compensation expense recognition period |  | 1 year 9 months 18 days |  |
2015 Plan |  |  |  |
Number of Shares |  |  |  |
Outstanding at the beginning (in shares) |  | 5,262,179 | 4,545,794 |
Granted (in shares) |  | 2,074,750 | 1,739,350 |
Exercised (in shares) |  | (5,057) | (50,420) |
Forfeitures (in shares) |  | (514,770) | (972,545) |
Outstanding at the end (in shares) |  | 6,817,102 | 5,262,179 | 4,545,794
Exercisable at the end (in shares) |  | 3,851,843 |  |
Weighted Average Exercise Price |  |  |  |
Outstanding at the beginning (in dollars per share) |  | $ 11.44 | $ 14.15 |
Granted (in dollars per share) |  | 1.55 | 5.34 |
Exercised (in dollars per share) |  | 0.99 | 1.32 |
Forfeited (in dollars per share) |  | 6.25 | 13.77 |
Outstanding at the end (in dollars per share) |  | 8.83 | $ 11.44 | $ 14.15
Exercisable at the end (in dollars per share) |  | $ 12.50 |  |
Weighted Average Remaining Contractual Life (Years) And Aggregate Intrinsic Value |  |  |  |
Outstanding (in years) |  | 7 years 3 months 18 days | 7 years 7 months 6 days | 8 years 1 month 6 days
Outstanding at the beginning (in dollars) |  | $ 115,000 | $ 2,860,000 |
Outstanding at the end (in dollars) |  |  | $ 115,000 | $ 2,860,000
Exercisable at the end (in dollars) |  | $ 52,000 |  |
Weighted average grant date fair value per share of stock options granted |  | $ 1.11 | $ 3.69 |
Aggregate intrinsic value of stock options exercised |  | $ 3,000 | $ 13,000 |
Aggregate grant date fair value |  | $ 9,100,000 | $ 11,000,000.0 |
Omnibus Incentive Plan |  |  |  |
Stock Based Compensation |  |  |  |
Number of shares reserved for issuance under the plan | 2,900,000 |  |  |
Annual increase in number of share reserved for issuance (as percent) | 4.00% |  |  |
2015 Plan and 2019 Employee Stock Purchase Plan |  |  |  |
Stock Based Compensation |  |  |  |
Vesting period |  | 4 years |  |
Expiration period |  | 10 years |  |
Number of shares reserved for issuance under the plan |  | 2,204,868 |  |
2019 Employee Stock Purchase Plan |  |  |  |
Stock Based Compensation |  |  |  |
Number of shares issued |  | 173,017 |  |
Number of shares reserved for issuance under the plan | 240,000 | 617,663 |  |
Annual increase in number of share reserved for issuance (as percent) | 1.00% |  |  |
Maximum annual increase in shares available for issuance under the plan | 480,000 |  |  |

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