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Goodwill - Summary of Carrying Amounts of Goodwill Allocated to Cash-generating Units (Detail)
$ in Thousands, $ in Thousands
Dec. 31, 2018
USD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2017
TWD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Disclosure of information for cash-generating units [line items]            
Goodwill $ 1,632,618 $ 49,974,446 $ 324,551 $ 9,934,494 $ 10,490,309 $ 10,506,519
Packaging segment [member]            
Disclosure of information for cash-generating units [line items]            
Goodwill 1,167,245 35,729,371   1,362,724    
Testing segment [member]            
Disclosure of information for cash-generating units [line items]            
Goodwill 439,362 13,448,886   7,775,581    
All other segments [member]            
Disclosure of information for cash-generating units [line items]            
Goodwill $ 26,011 $ 796,189   $ 796,189