Lessee, finance lease, additional lease expiration period.

No definition available.

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- Definition

Lessee, finance lease, expiration period.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Lessee, finance lease, option to extend the additional lease term.

+ References

No definition available.

+ Details

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Namespace Prefix:	fgen_
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Balance Type:	na
Period Type:	duration

- Definition

Lessee, operating lease, expiration period.

+ References

No definition available.

+ Details

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Namespace Prefix:	fgen_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of optional rights to extend lease.

+ References

No definition available.

+ Details

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Namespace Prefix:	fgen_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage increases on anniversary of rent commencement date option two.

+ References

No definition available.

+ Details

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Namespace Prefix:	fgen_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage increases on each anniversary of rent commencement date.

+ References

No definition available.

+ Details

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Namespace Prefix:	fgen_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Rent commencement year option one.

+ References

No definition available.

+ Details

Name:	fgen_ScheduledRentCommencementYearOptionOne
Namespace Prefix:	fgen_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Scheduled rent commencement year option two.

+ References

No definition available.

+ Details

Name:	fgen_ScheduledRentCommencementYearOptionTwo
Namespace Prefix:	fgen_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918701-209980

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of right-of-use asset from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
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-URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Indicates (true false) whether lessee has option to extend finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Description of terms and conditions of option to extend lessee's finance lease. Includes, but is not limited to, information about option recognized as part of right-of-use asset and lease liability.

+ References

+ Details

Name:	us-gaap_LesseeFinanceLeaseOptionToExtend
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's finance lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 45
-Paragraph 5
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-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918686-209980

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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- Details

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- Details

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Leases - Additional Information (Detail) $ in Thousands		3 Months Ended	12 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Jun. 01, 2021 USD ($) Option	Mar. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Lessee Lease Description [Line Items]
Finance lease right-of-use assets			$ 435	$ 761
Finance lease liability			173
Operating lease right-of-use assets			79,893	91,112
Operating lease liability			89,885
Cash payment related to lease			$ 15,497	10,022	$ 951
Minimum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, lease term			1 year
Maximum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, lease term			5 years
Office Spaces
Lessee Lease Description [Line Items]
Lessee, operating lease, expiration period			2025
Office Equipment [Member] \| Minimum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, lease term			1 year
Office Equipment [Member] \| Maximum [Member]
Lessee Lease Description [Line Items]
Lessee, operating lease, lease term			5 years
ASC 842 [Member]
Lessee Lease Description [Line Items]
Finance lease right-of-use assets			$ 0	24,654	0
Operating lease right-of-use assets			$ 0	$ 93,222	$ 0
Shorenstein Properties LLC [Member]
Lessee Lease Description [Line Items]
Lessee, finance lease, initial lease term			15 years
Lessee, finance lease, expiration period			2023
Shorenstein Properties LLC [Member] \| Lease Amendment [Member]
Lessee Lease Description [Line Items]
Lessee, finance lease, option to extend the additional lease term	5 years
Lessee, finance lease, additional lease expiration period	2028
Percentage increases on each anniversary of rent commencement date 2023	2.00%
Lessee, finance lease, existence of option to extend	true
Lessee, finance lease, option to extend	Under the terms of the Lease Amendment, the Company has two optional rights to each extend the lease for an additional five years.
Optional rights to extend lease \| Option	2
Rent increase commencement year first option	2023
Percentage increases on each anniversary of rent commencement date 2028	3.00%
Rent increase commencement year second option	2028
Shorenstein Properties LLC [Member] \| Lease Amendment [Member] \| ASC 842 [Member]
Lessee Lease Description [Line Items]
Finance lease right-of-use assets	$ 24,600
Finance lease liability	32,600
Operating lease right-of-use assets	93,200
Operating lease liability	$ 101,200
Beijing Economic-Technological Development Area [Member]
Lessee Lease Description [Line Items]
Operating lease right-of-use assets		$ 3,400
Operating lease liability		$ 3,400
Lessee, operating lease, lease term		5 years
Lessee, operating lease, expiration period		2026