Number of securities into which the class of warrant or right may be converted. For example, but not limited to, 500,000 warrants may be converted into 1,000,000 shares.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Name:	us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of expense (income) related to adjustment to fair value of warrant liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Section 25
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=109262497&loc=d3e20148-110875

+ Details

Name:	us-gaap_FairValueAdjustmentOfWarrants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the amount received from entity's raising of capital via private rather than public placement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfPrivatePlacement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow from issuance of rights to purchase common shares at predetermined price (usually issued together with corporate debt).

+ References

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfWarrants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the amount received from holders exercising their stock warrants.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromWarrantExercises
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of new stock issued during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of outstanding derivative securities that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_InvestmentTypeAxis=imab_InvestorWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=imab_CollaborationAgreementWithInvestoresMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=imab_HillhouseEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_SeriesBPreferredShareholdersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_SeriesBOnshoreInvestorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_TrancheIOfSeriesBWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_SeriesB2PreferredSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_TrancheIiOfSeriesBWarrantsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_SeriesBWarrantsSharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=imab_AmericanDepositarySharesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Warrants - Additional Information (Detail) $ / shares in Units, ¥ in Thousands					9 Months Ended			12 Months Ended
	Jul. 06, 2018 CNY (¥) shares	Jul. 06, 2018 USD ($) shares	Sep. 25, 2017 shares	Sep. 22, 2017 shares	Sep. 30, 2020 CNY (¥) shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 CNY (¥)	Dec. 31, 2020 CNY (¥)	Sep. 30, 2020 $ / shares	Jun. 29, 2018 shares	Oct. 31, 2016 $ / shares
Fair value gain of warrants for the year \| ¥							¥ (5,609)
Issuance of Private Placement					¥ 1,980,548	$ 291,703,000
Share price \| $ / shares											$ 0.77
Investor Warrants [Member]
Fair value of the Warrants \| ¥					¥ 71,874,000
Collaboration Agreement With Investores [Member]
Issuance of Private Placement \| $						418,000,000
Hillhouse Entities [Member]
Proceeds from issuance of warrants \| $						45.00
Series B Preferred Shareholders [Member]
Number of share issued, ADS				5,633,780
Series B Onshore Investors [Member]
Number of share issued, ADS			2,620,842
Tranche I Of Series B Warrants [Member]
Value of outstanding securities \| $						$ 20,000,000
Warrants issued and exercised	3,301,849	3,301,849
Series B2 Preferred Shares [Member]
Number of share issued, ADS					3,301,849	3,301,849
Value of outstanding securities	¥ 132,332	$ 20,000,000
Warrants issued and exercised										3,301,849
Tranche II of Series B Warrants [Member]
Value of outstanding securities \| $						$ 30,000,000
Series B Warrants Shares [Member]
Warrants issued and exercised	4,952,773	4,952,773
Fair value gain of warrants for the year \| ¥					¥ 5,609			¥ 0
American Depositary Shares [Member] \| Investor Warrants [Member]
Number of share issued, ADS					5,341,267	5,341,267
Share price \| $ / shares									$ 45
Proceeds from issuance of warrants \| $						$ 104,500,000