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Financial Risk Management and Fair Values of Financial Instruments - Details of Exposure to Currency Risk Arising from Recognized Monetary Assets or Liabilities Denominated in a Currency Other Than Functional Currency (Detail) - Currency Risk [member] - TWD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financial assets, class [member] | US$ [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Change in exchange rate	5.00%	5.00%	5.00%
Financial assets, class [member] | JPY [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Change in exchange rate	5.00%	5.00%	5.00%
Financial assets, class [member] | RMB [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Change in exchange rate	5.00%	5.00%	5.00%
Financial liabilities, class [member] | US$ [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Change in exchange rate	5.00%	5.00%	5.00%
Financial liabilities, class [member] | JPY [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Change in exchange rate	5.00%	5.00%	5.00%
Profit and Loss [member] | Financial assets, class [member] | US$ [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Effect of change in exchange rate	$ 250,396	$ 282,365	$ 261,492
Profit and Loss [member] | Financial assets, class [member] | JPY [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Effect of change in exchange rate	1,901	3,682	2,470
Profit and Loss [member] | Financial assets, class [member] | RMB [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Effect of change in exchange rate	1,497	1,334	1,979
Profit and Loss [member] | Financial liabilities, class [member] | US$ [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Effect of change in exchange rate	37,608	11,793	27,997
Profit and Loss [member] | Financial liabilities, class [member] | JPY [member]
Disclosure of nature and extent of risks arising from financial instruments [Line Items]
Effect of change in exchange rate	$ 21,251	$ 14,261	$ 33,887

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The amount of risk exposure associated with financial instruments with a shared characteristic that identifies a concentration of risks. [Refer: Financial instruments, class [member]]

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2020-01-01
-Paragraph B8
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_B8_c&doctype=Appendix&subtype=B
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