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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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- Definition The amount of risk exposure associated with financial instruments with a shared characteristic that identifies a concentration of risks. [Refer: Financial instruments, class [member]] + References 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 -URIDate 2020-01-01 + Details
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