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Subsequent Event - Additional Information (Detail) - USD ($) $ in Thousands | Jul. 19, 2021 | Jun. 30, 2021 | Dec. 31, 2020
--- | --- | --- | ---
Subsequent Event [Line Items] |  |  |
Deferred Revenue |  | $ 25,234 | $ 6,547
Subsequent Event [Member] | Eluminex [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Aggregate consideration received for milestone and upfront payments | $ 8,000 |  |
Future manufacturing clinical regulatory and commercial milestone payments | 64,000 |  |
Commercial milestone | $ 36,000 |  |
Drug Product Revenue [Member] |  |  |
Subsequent Event [Line Items] |  |  |
Deferred Revenue |  | $ 11,200 |

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- Definition Collaborative arrangement aggregate consideration for milestone and upfront payments. + References No definition available. + Details
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Namespace Prefix: | fgen_
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- Definition Commercial milestone. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Future manufacturing clinical regulatory and commercial milestone payments. + References No definition available. + Details
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Balance Type: | credit
Period Type: | duration

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- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130532-203044 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045 + Details
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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
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- Details
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- Details
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Namespace Prefix: |
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- Details
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