XML 116 R143.htm IDEA: XBRL DOCUMENT
v3.20.1

Retirement Benefit Plans - Additional Information (Detail) $ in Thousands, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 TWD ($) Unit | Dec. 31, 2019 USD ($) Unit | Dec. 31, 2018 TWD ($)
Disclosure of defined benefit plans [Line Items] |  |  |
Defined benefit plans expected contribution | $ 27,337 | $ 0 |
Weighted average duration of defined benefit obligation | 12 years 9 months 18 days | 12 years 9 months 18 days |
Defined benefit pension plan [Member] |  |  |
Disclosure of defined benefit plans [Line Items] |  |  |
Number of units accrued in first tranche | 2 | 2 |
Duration of first tranche | First 15 years | First 15 years |
Number of units accrued in second tranche | 1 | 1 |
Duration of second tranche | Thereafter 15 years | Thereafter 15 years |
Maximum number of units accruable under the pension plan | 45 | 45 |
Benefit measurement period | 6 months | 6 months |
Employer contribution percentage | 2.00% | 2.00% |
Defined contribution pension plan [member] |  |  |
Disclosure of defined benefit plans [Line Items] |  |  |
Employer contribution percentage | 6.00% | 6.00% | 6.00%
Pension costs under defined contribution pension plans | $ | $ 187,502 |  | $ 193,047

X
- 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_DisclosureOfDefinedBenefitPlansLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 147 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_147_b&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 148 -Subparagraph d -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_148_d_iii&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_EstimateOfContributionsExpectedToBePaidToPlan
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The amount of post-employment benefit expense relating to defined contribution plans. Defined contribution plans are post-employment benefit plans under which an entity pays fixed contributions into a separate entity (a fund) and will have no legal or constructive obligation to pay further contributions if the fund does not hold sufficient assets to pay all employee benefits relating to employee service in the current and prior periods. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 53 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_53&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_PostemploymentBenefitExpenseDefinedContributionPlans
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The weighted average duration of a defined benefit obligation. [Refer: Weighted average [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2019-01-01 -Paragraph 147 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2019-en-r&anchor=para_147_c&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_WeightedAverageDurationOfDefinedBenefitObligation2019
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Benefit measurement period. + References No definition available. + Details
Name: | imos_BenefitMeasurementPeriod
Namespace Prefix: | imos_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined contribution plans employer contribution percentage. + References No definition available. + Details
Name: | imos_DefinedContributionPlansEmployerContributionPercentage
Namespace Prefix: | imos_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Duration of first tranche. + References No definition available. + Details
Name: | imos_DurationOfFirstTranche
Namespace Prefix: | imos_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Duration of second tranche. + References No definition available. + Details
Name: | imos_DurationOfSecondTranche
Namespace Prefix: | imos_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Maximum number of units accruable under the pension plan. + References No definition available. + Details
Name: | imos_MaximumNumberOfUnitsAccruableUnderThePensionPlan
Namespace Prefix: | imos_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of units accrued in first tranche. + References No definition available. + Details
Name: | imos_NumberOfUnitsAccruedInFirstTranche
Namespace Prefix: | imos_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of units accrued in second tranche. + References No definition available. + Details
Name: | imos_NumberOfUnitsAccruedInSecondTranche
Namespace Prefix: | imos_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_DefinedBenefitPlansAxis=ifrs-full_DefinedBenefitPlansOtherThanMultiemployerPlansStatePlansAndPlansThatShareRisksBetweenEntitiesUnderCommonControlMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_DefinedBenefitPlansAxis=imos_DomesticDefinedContributionPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |