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Significant contingent liabilities and unrecognized contract commitments - Additional Information (Detail) - TWD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Capital commitments [abstract] |  |
Amount guaranteed by Bank of Taiwan | $ 99,000 | $ 100,800

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- References No definition available. + Details
Name: | ifrs-full_CapitalCommitmentsAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Bank guarantees. + References No definition available. + Details
Name: | imos_BankGuarantees
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant