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Long-term Bank Loans - Additional Information (Detail) $ in Millions		3 Months Ended
	May 15, 2018 TWD ($) Bank	Mar. 31, 2020 TWD ($)
Maximum [Member]
Disclosure of detailed information about borrowings [Line Items]
Maturity of loan		ten years
Minimum [Member]
Disclosure of detailed information about borrowings [Line Items]
Maturity of loan		seven years
Syndicated loan [member]
Disclosure of detailed information about borrowings [Line Items]
Number of banks in syndicate | Bank	11
Principal amount of loan	$ 12,000
Maturity of loan	five years
Government granted bank loans [Member]
Disclosure of detailed information about borrowings [Line Items]
Principal amount of loan		$ 12,144

X

- Definition

The maturity of borrowings. [Refer: Borrowings]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 7
-IssueDate 2020-01-01
-Paragraph 7
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-URIDate 2020-01-01

+ Details

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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

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X

- Definition

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2020-01-01

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

Number of banks in syndicate.

+ References

No definition available.

+ Details

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Namespace Prefix:	imos_
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Balance Type:	na
Period Type:	duration

X

- Details

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X

- Details

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X

- Details

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Balance Type:
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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: