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Goodwill - Additional Information (Detail) - TWD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2019
Dec. 31, 2018
Disclosure of reconciliation of changes in goodwill [line items]      
Impairment loss on goodwill $ 425,117    
Bottom of range [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Discount rate applied to cash flow projections 10.82% 9.59% 9.74%
Top of range [member]      
Disclosure of reconciliation of changes in goodwill [line items]      
Discount rate applied to cash flow projections 12.42% 14.99% 10.22%