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Income Taxes - Summary of Statutory Tax Rates Applicable to Income of Company and Subsidiaries (Details) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Income Tax Disclosure [Line Items] |  |
Effective income tax rate | 21.00% | 21.00%
89Bio Ltd |  |
Income Tax Disclosure [Line Items] |  |
Effective income tax rate | 23.00% | 23.00%
89bio Management, Inc. |  |
Income Tax Disclosure [Line Items] |  |
Effective income tax rate | 21.00% | 21.00%
UAB 89bio Lithuania |  |
Income Tax Disclosure [Line Items] |  |
Effective income tax rate | 15.00% | 15.00%

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- Definition Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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