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Retirement Benefit Plans - Summary of Defined Benefit Plans Amounts Included in Consolidated Balance Sheets (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2018 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($) | Dec. 31, 2015 TWD ($)
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Disclosure of net defined benefit liability (asset) [abstract] |  |  |  |  |  |
Present value of the defined benefit obligation | $ 336,398 | $ 10,297,139 |  | $ 7,910,638 |  |
Fair value of the plan assets | (179,423) | (5,492,123) |  | (4,341,373) |  |
Present value of unfunded defined benefit obligation | 156,975 | 4,805,016 | $ 116,604 | 3,569,265 | $ 3,972,517 | $ 3,999,947
Recorded under other payables | (614) | (18,791) |  | (24,638) |  |
Recorded under other current assets | 389 | 11,910 |  | 182,421 |  |
Net defined benefit liability | $ 156,750 | $ 4,798,135 |  | $ 3,727,048 |  |

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- Definition Defined benefit plan recorded under others payables. + References No definition available. + Details
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- Definition Net defined benefit liability. + References No definition available. + Details
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- Definition Recorded under other current assets. + References No definition available. + Details
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- Definition The present value, without deducting any plan assets, of expected future payments required to settle the obligation resulting from employee service in the current and prior periods. [Refer: Plan assets, at fair value] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 57 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_57_a&doctype=Standard -URIDate 2018-03-16 + Details
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- References No definition available. + Details
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- Definition The amount of deficit or surplus in a defined benefit plan, adjusted for any effect of limiting a net defined benefit asset to the asset ceiling. [Refer: Defined benefit plans [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 140 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_140_a&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2018-01-01 -Paragraph 57 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2018-03-01&anchor=para_57_a&doctype=Standard -URIDate 2018-03-16 + Details
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