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Commitments and Contingencies - Additional Information (Detail) $ in Millions | 6 Months Ended
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Jun. 30, 2020 USD ($)
Commitments And Contingencies [Line Items] |
Outstanding non-cancelable contract obligations | $ 26.2
Manufacture and Supply of Roxadustat [Member] |
Commitments And Contingencies [Line Items] |
Outstanding non-cancelable contract obligations | 14.2
Research and Pre-Clinical Stage Development Programs [Member] |
Commitments And Contingencies [Line Items] |
Future milestone payments | 10.9
Other Purchases [Member] |
Commitments And Contingencies [Line Items] |
Outstanding non-cancelable contract obligations | $ 1.1

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- Definition Commitments and contingencies. + References No definition available. + Details
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Data Type: | xbrli:stringItemType
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- Definition Future milestone payments. + References No definition available. + Details
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Namespace Prefix: | fgen_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |