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FibroGen, Inc. 401(k) Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	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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- References

No definition available.

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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

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- Definition

Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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