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FibroGen, Inc. 401(k) Plan - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract] |  |  |
Defined contribution plan, maximum annual contributions per employee, percent | 60.00% |  |
Defined contribution plan, employer matching contributions | $ 3.2 | $ 3.0 | $ 2.9

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan. + References No definition available. + Details
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