XML 37 R26.htm IDEA: XBRL DOCUMENT v3.21.2

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jan. 01, 2021
Accounting Policies [Abstract]
Lease liability	$ 47,746	$ 49,700
Operating lease right-of-use assets	31,988	$ 33,400
Market value threshold to qualify as an emerging growth company	$ 700,000

X

- Definition

Market value threshold to qualify as an emerging growth company

+ References

No definition available.

+ Details

Name:	gbio_MarketValueThresholdToQualifyAsEmergingGrowthCompany
Namespace Prefix:	gbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- 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 http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

+ Details

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

X

- Definition

Amount of lessee's right to use underlying asset under 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 (a)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

+ Details

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