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v3.21.1

Leasing arrangements - leasee - Additional Information (Detail) - TWD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Statement [line items] |  |
Additions to right of use asset | $ 261,798 | $ 11,183
Payments of lease liabilities | $ 274,727 | $ 273,709
Top of range [member] |  |
Statement [line items] |  |
Lease term | 30 years |
Bottom of range [member] |  |
Statement [line items] |  |
Lease term | 2 years |

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- Definition The amount of additions to right-of-use assets. [Refer: Right-of-use assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 16 -IssueDate 2020-01-01 -Paragraph 53 -Subparagraph h -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2020-en-r&anchor=para_53_h&doctype=Standard -URIDate 2020-01-01 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The cash outflow for leases. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 16 -IssueDate 2020-01-01 -Paragraph 53 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2020-en-r&anchor=para_53_g&doctype=Standard -URIDate 2020-01-01 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Lease term. + References No definition available. + Details
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Namespace Prefix: | imos_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |