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FibroGen, Inc. 401(k) Plan - Additional Information (Detail) - USD ($) | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Compensation And Retirement Disclosure [Abstract] |  |  |
Defined contribution plan, maximum annual contributions per employee, percent | 60.00% |  |
Defined contribution plan, employer matching contributions | $ 2,500,000 | $ 1,900,000 | $ 0

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- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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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