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Income Tax Expense - Additional Information (Detail) - TWD ($)
$ in Thousands
 3 Months Ended
Oct. 31, 2016
Jun. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Disclosure of income tax expense [Line Items]        
Taxable temporary differences not recognized as deferred tax liaibility     $ 45,005 $ 180,395
Reduction of unappropriated retained earnings through capital transfer $ 5,052,343      
Income taxes paid (refund)   $ 138,941