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Goodwill - Summary of Carrying Amounts of Goodwill Allocated to Cash-generating Units (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 information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | $ 1,632,618 | $ 49,974,446 | $ 324,551 | $ 9,934,494 | $ 10,490,309 | $ 10,506,519
Packaging segment [member] |  |  |  |  |  |
Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | 1,167,245 | 35,729,371 |  | 1,362,724 |  |
Testing segment [member] |  |  |  |  |  |
Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | 439,362 | 13,448,886 |  | 7,775,581 |  |
All other segments [member] |  |  |  |  |  |
Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | $ 26,011 | $ 796,189 |  | $ 796,189 |  |

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- Definition The amount of assets representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognised. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph B67 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_B67_d&doctype=Appendix&seq=2 -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2018-01-01 -Paragraph 134 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2018-03-01&anchor=para_134_a&doctype=Standard -URIDate 2018-03-16 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2018-01-01 -Paragraph 135 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2018-03-01&anchor=para_135_a&doctype=Standard -URIDate 2018-03-16 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 54 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_54_c&doctype=Standard -URIDate 2018-03-16 + Details
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