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Pensions - Additional Information (Detail) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 TWD ($) Unit | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($)
Disclosure of defined benefit plans [Line Items] |  |  |
Defined benefit plans expected contribution | $ | $ 26,261 |  |
Weighted average duration of defined benefit obligation | 12 years 7 months 6 days |  |
Defined benefit pension plan [Member] |  |  |
Disclosure of defined benefit plans [Line Items] |  |  |
Number of units accrued in first tranche | 2 |  |
Duration of first tranche | First 15 years |  |
Number of units accrued in second tranche | 1 |  |
Duration of second tranche | Thereafter 15 years |  |
Maximum number of units accruable under the pension plan | 45 |  |
Benefit measurement period | 6 months |  |
Employer contribution percentage | 2.00% |  |
Defined contribution pension plan [member] |  |  |
Disclosure of defined benefit plans [Line Items] |  |  |
Employer contribution percentage | 6.00% | 6.00% |
Pension costs under defined contribution pension plans | $ | $ 184,562 | $ 187,502 | $ 193,047

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- Definition The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 147 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_147_b&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 148 -Subparagraph d -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_148_d_iii&doctype=Standard -URIDate 2020-01-01 + Details
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