| Share-Based Payment Arrangement, Option, Activity [Table Text Block] |
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Weighted- |
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Weighted- |
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Average |
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Aggregate |
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Average |
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Remaining |
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Intrinsic |
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Number of |
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Exercise |
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Contractual |
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Value |
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Options |
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Price |
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Life (in years) |
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(in thousands) |
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| Outstanding, December 31, 2022 |
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13,430,366 |
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$ |
3.21 |
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$ |
— |
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| Granted |
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3,727,942 |
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1.22 |
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— |
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| Canceled/Forfeited |
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2,655,237 |
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2.65 |
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— |
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| Outstanding, December 31, 2023 |
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14,503,071 |
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$ |
2.80 |
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5.90 |
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$ |
— |
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| Vested or expected to vest, December 31, 2023 |
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14,503,071 |
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$ |
2.80 |
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5.90 |
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$ |
— |
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| Exercisable, December 31, 2023 |
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10,292,063 |
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$ |
3.21 |
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4.75 |
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$ |
— |
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Weighted- |
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Weighted- |
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Average |
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Aggregate |
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Average |
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Remaining |
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Intrinsic |
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Number of |
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Exercise |
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Contractual |
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Value |
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Options |
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Price |
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Life (in years) |
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(in thousands) |
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| Outstanding, December 31, 2022 |
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300,000 |
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$ |
4.65 |
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$ |
— |
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| Granted |
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— |
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$ |
— |
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$ |
— |
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| Canceled/Forfeited |
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— |
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$ |
— |
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$ |
— |
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| Outstanding, December 31, 2023 |
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300,000 |
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$ |
4.65 |
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5.67 |
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$ |
— |
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| Vested or expected to vest, December 31, 2023 |
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300,000 |
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$ |
4.65 |
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5.67 |
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$ |
— |
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| Exercisable, December 31, 2023 |
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300,000 |
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$ |
4.65 |
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5.67 |
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$ |
— |
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| Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] |
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Years Ended December 31, |
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2023 |
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2022 |
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| Research and development |
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$ |
1,190 |
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$ |
1,905 |
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| General and administrative |
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2,159 |
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2,497 |
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| Total stock-based compensation |
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$ |
3,349 |
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$ |
4,402 |
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