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v3.20.1

Related Party Transactions - Summary of Significant Related Party Transactions (Detail) - TWD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Unimos Shanghai [member] |  |
Disclosure of transactions between related parties [Line Items] |  |
Subcontracting fee | $ 17 | $ 41,183

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
Name: | ifrs-full_DisclosureOfTransactionsBetweenRelatedPartiesLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Subcontracting fee, related party transactions. + References No definition available. + Details
Name: | imos_SubcontractingFeeRelatedPartyTransactions
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | ifrs-full_SignificantInvestmentsInAssociatesAxis=imos_UnimosShanghaiMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |