Revenue - Summary of Contract Assets and Liabilities (Detail) - TWD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Disclosure of contract assets and liabilities in relation to revenue [Abstract]
Contract assets	$ 389,016	$ 377,869	$ 299,835
Contract liabilities (Advance payments)		$ 1,231	$ 1,432

The amount of an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer, when that right is conditioned on something other than the passage of time (for example, the entity’s future performance).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 105
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_105&doctype=Standard
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 15
-IssueDate 2020-01-01
-Paragraph 116
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=15&code=ifrs-tx-2020-en-r&anchor=para_116_a&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_ContractAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration (or the amount is due) from the customer.

+ References

+ Details

Name:	ifrs-full_ContractLiabilities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Disclosure of contract assets and liabilities in relation to revenue.

+ References

No definition available.

+ Details

Name:	imos_DisclosureOfContractAssetsAndLiabilitiesInRelationToRevenueAbstract
Namespace Prefix:	imos_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration