Financial Instruments - Summary of Fair Value of Financial Instruments Not Measured at Fair Value but for Which Fair Value is Disclosed (Detail) $ in Thousands, $ in Thousands	Dec. 31, 2020 TWD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 TWD ($)
Disclosure of detailed information about financial instruments [line items]
Bonds payable	$ 56,253,554	$ 2,003,332	$ 36,522,155
Fair value [member]
Disclosure of detailed information about financial instruments [line items]
Bonds payable	$ 56,448,769	$ 2,010,284	$ 36,766,117

The amount of bonds issued by the entity.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_BondsIssued
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant