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Significant Events After the Reporting Periods - Additional Information (Detail) - Line of credit [member] - TWD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2019
Bottom of range [member] |  |
Disclosure of events after reporting period [Line Items] |  |
Line of credit term |  | seven years
Top of range [member] |  |
Disclosure of events after reporting period [Line Items] |  |
Line of credit term |  | ten years
MOEA [member] |  |
Disclosure of events after reporting period [Line Items] |  |
Borrowings line of credit | $ 12,144 |
Increase decrease in line of credit | $ 3,584 |

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- Definition The maturity of borrowings. [Refer: Borrowings] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_7&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_BorrowingsMaturity
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Borrowings line of credit. + References No definition available. + Details
Name: | imos_BorrowingsLineOfCredit
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Cash flows from used in increase decrease in line of credit. + References No definition available. + Details
Name: | imos_CashFlowsFromUsedInIncreaseDecreaseInLineOfCredit
Namespace Prefix: | imos_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Disclosure of events after reporting period line items. + References No definition available. + Details
Name: | imos_DisclosureOfEventsAfterReportingPeriodLineItems
Namespace Prefix: | imos_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | ifrs-full_BorrowingsByNameAxis=imos_LineOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | ifrs-full_NonadjustingEventsAfterReportingPeriodAxis=imos_MinistryOfEconomicAffairsRocMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |