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Convertible Note Payable - Additional Information (Detail) - FibroGen China [Member] - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jan. 31, 2013 | Dec. 31, 2017
Debt Instrument [Line Items] |  |
Convertible promissory note | $ 0.6 |
Interest rate of convertible promissory note | 2.00% |
Anniversary date of promissory note |  | 8 years

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