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Intangible Assets - Additional Information (Detail) - TWD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2019
Dec. 31, 2018
Disclosure of reconciliation of changes in intangible assets and goodwill [abstract]      
Annual discount rate   8.00% 9.00%
Impairment loss recognized in goodwill $ 13.5