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%

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]

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

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant