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Retained Earnings - Details of Retained Earnings (Detail) - TWD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of analysis of other comprehensive income by item [line items]
Cash dividend, cash distribution per share	$ 2.20	$ 1.80	$ 1.20
Legal reserve [member]
Disclosure of analysis of other comprehensive income by item [line items]
Appropriation of retained earnings	$ 232,611	$ 258,416	$ 110,308
Special Reserve [Member]
Disclosure of analysis of other comprehensive income by item [line items]
Appropriation of retained earnings	(19,802)	19,802
Cash Dividend [Member]
Disclosure of analysis of other comprehensive income by item [line items]
Appropriation of retained earnings	$ 1,599,928	$ 1,309,032	$ 872,718

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

+ References

No definition available.

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- Definition

The amount of dividends paid per ordinary share.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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-IssueDate 2021-01-01
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- Definition

The increase (decrease) in equity resulting from the appropriation of retained earnings. [Refer: Retained earnings]

+ References

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-IssueDate 2021-01-01
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