The amount of outstanding funds that the entity is obligated to repay.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 55
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-URIDate 2020-01-01

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

- Definition

The interest rate on 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

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Balance Type:	na
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- Definition

The current portion of non-current borrowings. [Refer: Borrowings]

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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.

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- Definition

The non-current portion of non-current borrowings. [Refer: Borrowings]

+ References

+ Details

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

- Definition

The amount of undrawn borrowing facilities that may be available for future operating activities and to settle capital commitments. [Refer: Capital commitments]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2020-01-01
-Paragraph 50
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-URIDate 2020-01-01

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Borrowing repayable period.

+ References

No definition available.

+ Details

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

- Definition

The amount of fee on syndicated bank loan.

+ References

No definition available.

+ Details

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Namespace Prefix:	imos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Unamortized interest on government granted bank loans

+ References

No definition available.

+ Details

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Namespace Prefix:	imos_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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- Details

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Long-term Bank Loans - Summary of Long-term Bank Loans (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 TWD ($)	Dec. 31, 2019 TWD ($)	Dec. 31, 2020 USD ($)
Disclosure of detailed information about borrowings [Line Items]
Bank loans	$ 7,733,565	$ 9,041,645
Less:Fee on syndicated bank loan	(17,223)	(24,355)
Less: Unamortized interest on government granted bank loans	(64,212)
Less: Current portion (fee included)	(748,353)	(748,419)	$ (26,651)
Syndicated bank loans, excluding current portion	6,985,212	8,293,226	$ 248,761
Long-term bank loans [Member]
Disclosure of detailed information about borrowings [Line Items]
Unused credit lines of long-term	$ 11,239,000	$ 1,800,000
Gross carrying amount [member]
Disclosure of detailed information about borrowings [Line Items]
Interest rate range		1.7895%
Gross carrying amount [member] \| Minimum [Member]
Disclosure of detailed information about borrowings [Line Items]
Interest rate range	0.65%		0.65%
Gross carrying amount [member] \| Maximum [Member]
Disclosure of detailed information about borrowings [Line Items]
Interest rate range	1.7895%		1.7895%
Gross carrying amount [member] \| Syndicated bank loans repayable from November 2018 to May 2023 [member]
Disclosure of detailed information about borrowings [Line Items]
Bank loans	$ 3,310,000	$ 9,066,000
Period and payment term	Borrowing period is from May 30, 2018 to May 30, 2023; interest is repayable monthly; principal is repayable semi-annually from November 30, 2018	Borrowing period is from May 30, 2018 to May 30, 2023; interest is repayable monthly; principal is repayable semi-annually from November 30, 2018
Gross carrying amount [member] \| Government granted bank loans from March 2020 To February 2030 [Member]
Disclosure of detailed information about borrowings [Line Items]
Bank loans	$ 4,505,000
Period and payment term	Borrowing period is from March 11, 2020 to February 15, 2030; interest is repayable monthly; principal is repayable monthly from March 15, 2023