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Financial Instruments - Summary of Detailed Information About Hedges Items (Detail)
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2020
USD ($)
Borrowings denominated in foreign currencies [member]        
Disclosure of detailed information about hedged items [line items]        
Change in Value Used for Calculating Hedge Ineffectiveness, Hedging Instrument     $ 71,743  
Hedged item, assets $ 2,859,132   2,791,574 $ 101,821
Accumulated Amount of Fair Value Hedge Adjustments on Hedged Item, Asset     15,625  
Fair value hedge of borrowings denominated in foreign currencies [member]        
Disclosure of detailed information about hedged items [line items]        
Change in Value Used for Calculating Hedge Ineffectiveness, Hedging Instrument 157,842 $ 5,621    
Hedged item, assets (157,842)     (5,621)
Accumulated Amount of Fair Value Hedge Adjustments on Hedged Item, Asset (142,217)     (5,065)
Hedges of net investment in foreign operations [member]        
Disclosure of detailed information about hedged items [line items]        
Change in Value Used for Calculating Hedge Ineffectiveness, Hedging Instrument 574,824 $ 20,471    
Hedged item, assets (574,824)   $ (71,743) (20,471)
Accumulated Gains or Losses in Other Equity, Continuing Hedges $ (574,824)     $ (20,471)