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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

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_DisclosureOfTransactionsBetweenRelatedPartiesLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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

X

- Details

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