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Related Parties - Additional Information (Detail) - Mosaic - Intravitreal Anti-Complement Factor 3 - USD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Jan. 10, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Subsequent Event |  |  |
Related Party Transaction [Line Items] |  |  |
Payment related to collaboration | $ 3.0 |  |
Collaboration Agreement |  |  |
Related Party Transaction [Line Items] |  |  |
Expenses related to collaboration |  | $ 1.1 | $ 1.3
Biogen Collaboration | Subsequent Event |  |  |
Related Party Transaction [Line Items] |  |  |
Upfront license fee received from collaboration agreement | $ 15.0 |  |

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