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Significant Contingent Liabilities and Unrecognized Commitments - Additional Information (Detail)
$ in Thousands, $ in Thousands
 1 Months Ended 12 Months Ended
Dec. 31, 2013
TWD ($)
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2013
USD ($)
Disclosure of contingent liabilities [line items]            
Unused letters of credit   $ 2,000   $ 394,000 $ 71  
Committed to purchase property, plant and equipment   32,627,411   25,119,371 1,161,945  
Prepayment of property, plant and equipment   1,968,779 $ 70,113 5,145,345    
Construction contract related to real estate business   602,548 $ 21,458 1,393,859    
Letter of credits   $ 671,721   $ 952,001 $ 23,922  
Taiwan [member]            
Disclosure of contingent liabilities [line items]            
Contractual period for environmental protection 30 years          
Contribution to be made for environmental protection $ 3,000,000         $ 106,838