Financial Assets at Fair Value Through Other Comprehensive Income - Additional Information (Detail) - TWD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financial assets at fair value through other comprehensive income [abstract]
Proceeds from sale of shares	$ 10	$ 873,500	$ 840,600
Unrealized gain (loss) on investments in equity instruments at fair value through other comprehensive income	109,000	156,800	$ 1,193,100
Cumulative loss allowance for expected credit loss	$ 32,500	$ 35,600

The cash inflow from issuing shares.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2020-01-01
-Paragraph 17
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=7&code=ifrs-tx-2020-en-r&anchor=para_17_a&doctype=Standard
-URIDate 2020-01-01

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration