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Significant Commitments and Contingencies - Future Minimum Lease Obligation Payable under Operating Lease Contracts (Detail) $ in Thousands	Dec. 31, 2018 TWD ($)
Disclosure of finance lease and operating lease by lessee [Line Items]
Minimum finance lease payments payable	$ 320,214
Within 1 year [member]
Disclosure of finance lease and operating lease by lessee [Line Items]
Minimum finance lease payments payable	68,631
1-5 years [member]
Disclosure of finance lease and operating lease by lessee [Line Items]
Minimum finance lease payments payable	140,137
Over 5 years [member]
Disclosure of finance lease and operating lease by lessee [Line Items]
Minimum finance lease payments payable	$ 111,446

X

- Definition

Disclosure of lessee.

+ References

No definition available.

+ Details

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

X

- Definition

The amount of future minimum lease payments payable under non-cancellable operating leases.

+ References

No definition available.

+ Details

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Namespace Prefix:	imos_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

Name:	ifrs-full_MaturityAxis=ifrs-full_NotLaterThanOneYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_MaturityAxis=ifrs-full_LaterThanOneYearAndNotLaterThanFiveYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_MaturityAxis=ifrs-full_LaterThanFiveYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: