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Commitments and Contingencies - Additional Information (Details) - USD ($) | 1 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2015 | Oct. 31, 2014 | Dec. 31, 2020 | Dec. 31, 2019
Loss Contingencies [Line Items] |  |  |  |
Rent expense |  |  | $ 732,000 | $ 696,000
Operating expenses |  |  | 29,832,000 | 37,502,000
Accounts payable |  |  | 2,513,000 | 4,636,000
JHU |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Operating expenses |  |  | 203,000 | 395,000
License Agreement | JHU |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
One-time, non-refundable fee | $ 100,000 |  |  |
Maximum credit percentage of running royalty rate | 50.00% |  |  |
Kala Agreement |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage of minimum annual royalties including development milestone payments for first licensed product |  | 25.00% |  |
Development milestone payment extension period |  | 1 year |  |
Development milestone payable under second licensed product |  | $ 100,000 |  |
Development milestone payable under third licensed product |  | $ 150,000 |  |
Operating expenses |  |  | 0 | 0
Accounts payable |  |  | 0 | 0
AffaMed Letter |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Operating expenses |  |  | 0 | 0
Accounts payable |  |  | $ 0 | $ 0
Option expiration period |  |  | Jul. 31, 2021 |
Collaborative arrangement, description |  |  | The AffaMed Letter provides AffaMed with an initial 30-day period to propose terms for such a license which, if such terms are approved by a majority of the Company’s board of directors (excluding the director originally appointed by AffaMed and who continues to serve on our board), shall lead to a 60-day exclusive negotiation period. During this period of up to 90 days, the Company is prohibited from soliciting, initiating, encouraging or assisting the submission of any other proposal, negotiation or offer for the development, registration and commercialization of GB-102 in China, Hong Kong, Taiwan, Macau or South Korea. |
Redwood City, California |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Operating lease, term |  |  | 2021-08 |
Baltimore, Maryland |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Operating lease, term |  |  | 2023-06 |
United States | Kala Agreement |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage of commercial milestone payments reduced |  | 50.00% |  |
Minimum | License Agreement | JHU |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Percentage of royalty payments on net sales | 50.00% |  |  |
Percentage of developmental milestone payment for second and third products | 50.00% |  |  |
Maximum | License Agreement | JHU |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Aggregate total amount of developmental milestone payment | $ 2,000,000 |  |  |
Research and Development |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Contractual obligation |  |  | $ 7,700,000 |
Research and Development | Minimum |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Contractual obligation term |  |  | 3 months |
Research and Development | Maximum |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Contractual obligation term |  |  | 15 months |

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