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Income Tax - Additional Information (Detail) $ in Thousands, $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 | Dec. 31, 2018 TWD ($)
Disclosure of income taxes [line items] |  |  |  |
Applied tax rate | 20.00% | 17.00% | 17.00% |
Income tax on unappropriated earnings | 5.00% | 10.00% |  |
Taxable temporary differences associated with the investments in subsidiaries for which no deferred tax liabilities recognized | $ 941,224 | $ 16,401,422 |  | $ 28,810,874
Subsidiaries [member] | China [member] |  |  |  |
Disclosure of income taxes [line items] |  |  |  |
Applied tax rate | 25.00% | 25.00% |  |
Reduction tax rate | 15.00% |  |  |

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- Definition The applicable income tax rate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2018-01-01 -Paragraph 81 -Subparagraph c -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2018-03-01&anchor=para_81_c_ii&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The aggregate amount of temporary differences associated with investments in subsidiaries, branches and associates and interests in joint arrangements, for which deferred tax liabilities have not been recognised as a result of satisfying both of the following conditions: (a) the parent, investor, joint venturer or joint operator is able to control the timing of the reversal of the temporary difference; and (b) it is probable that the temporary difference will not reverse in the foreseeable future. [Refer: Associates [member]; Subsidiaries [member]; Temporary differences [member]; Investments in subsidiaries] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2018-01-01 -Paragraph 81 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=12&date=2018-03-01&anchor=para_81_f&doctype=Standard -URIDate 2018-03-16 + Details
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