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Goodwill - Summary of Carrying Amounts of Goodwill Allocated to Cash-generating Units (Detail)
$ in Thousands, $ in Thousands
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
TWD ($)
Disclosure of information for cash-generating units [line items]            
Goodwill $ 54,777,439 $ 1,950,764 $ 50,198,436 $ 1,787,693 $ 49,974,446 $ 9,934,494
Packaging segment [member]            
Disclosure of information for cash-generating units [line items]            
Goodwill 35,703,625 1,271,496 35,717,828      
Testing segment [member]            
Disclosure of information for cash-generating units [line items]            
Goodwill 13,365,068 475,964 13,421,321      
EMS Segment Member [Member]            
Disclosure of information for cash-generating units [line items]            
Goodwill 5,560,645 198,029 903,346      
All other segments [member]            
Disclosure of information for cash-generating units [line items]            
Goodwill $ 148,101 $ 5,275 $ 155,941