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Pensions - Defined Benefit Plans Amounts Recognized in Statements of Financial Position (Detail) - TWD ($)
$ in Thousands
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Surplus (deficit) in plan [abstract]        
Present value of defined benefit obligations $ (959,677) $ (943,391)    
Fair value of plan assets 456,389 431,740    
Net defined benefit liability $ (503,288) $ (511,651) $ (480,107) $ (520,765)