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Related Party Balances and Transactions - Summary of Related Party Balances (Detail) ¥ in Thousands, $ in Thousands	Sep. 30, 2020 CNY (¥)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 CNY (¥)
Related Party Transaction [Line Items]
Ordinary shares to be issued to Everest			¥ 258,119
Loans to an affiliate	¥ 52,000	$ 7,659
I-Mab Hangzhou [Member]
Related Party Transaction [Line Items]
Loans to an affiliate	52,000	7,659	0
Everest [Member]
Related Party Transaction [Line Items]
Ordinary shares to be issued to Everest	¥ 0	$ 0	¥ 258,119

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Common stock shares issuable for services availed current.

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- Definition

Amount of receivables due from an entity that is affiliated with the reporting entity by means of direct or indirect ownership, due within 1 year (or 1 business cycle).

+ References

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- 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.

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