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Inventories - Cost of Inventories Recognized as an Expense (Detail)
$ in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2019
TWD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
TWD ($)
Analysis of income and expense [abstract]        
Cost of revenue $ 16,372,032   $ 15,057,605  
Loss on abandonment 12,369   5,497  
Allowance for (reversal of) inventory valuation and obsolescence loss 27,341   (13,070)  
Cost of revenue $ 16,411,742 $ 548,704 $ 15,050,032 $ 14,703,729