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v3.20.1

Current Refund Liabilities - Summary of Movements in Refund Liabilities (Detail) - TWD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Disclosure of refund liability [abstract] |  |
Beginning balance | $ 32,627 | $ 70,156
Provision | 63,863 | 44,950
Reversal |  | (7,413)
Payment | (70,490) | (75,066)
Ending balance | $ 26,000 | $ 32,627

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- Definition Disclosure of refund liability [abstract] + References No definition available. + Details
Name: | imos_DisclosureOfRefundLiabilityAbstract
Namespace Prefix: | imos_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Payment of refund liabilities - current. + References No definition available. + Details
Name: | imos_PaymentOfRefundLiabilitiesCurrent
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Provisions for refund liabilities - current. + References No definition available. + Details
Name: | imos_ProvisionsForRefundLiabilitiesCurrent
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Provisions for sales allowance, refund liabilities - current. + References No definition available. + Details
Name: | imos_ProvisionsForSalesAllowanceRefundLiabilitiesCurrent
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Reversal of refund liabilities - current. + References No definition available. + Details
Name: | imos_ReversalOfRefundLiabilitiesCurrent
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration