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Investments Accounted for Using the Equity Method - Summary of Investments in Associates Accounted for Using the Equity Method (Detail)
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2020
TWD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2020
USD ($)
Disclosure of associates and joint ventures [line items]      
Investments in associates $ 12,335,239 $ 11,805,505 $ 439,289
Yann Yuan Investment Co., Ltd. [member]      
Disclosure of associates and joint ventures [line items]      
Main Business Engaged in investing activities    
Operating Location R.O.C.    
Percentages of ownership held by the Group 32.21% 32.21%  
ChipMOS Technologies Inc. [member]      
Disclosure of associates and joint ventures [line items]      
Main Business Engaged in the packaging and testing of semiconductors    
Operating Location R.O.C.    
Percentages of ownership held by the Group 10.85% 20.48%  
M-Universe Investments Pte. Ltd. [member]      
Disclosure of associates and joint ventures [line items]      
Main Business Investment company    
Operating Location Singapore    
Percentages of ownership held by the Group 42.23% 42.23%  
Hung Ching Development & Construction Co. [member]      
Disclosure of associates and joint ventures [line items]      
Main Business Engaged in the development, construction and leasing of real estate properties    
Operating Location R.O.C.    
Percentages of ownership held by the Group 26.22% 26.22%  
Hung Ching Kwan Co. [member]      
Disclosure of associates and joint ventures [line items]      
Main Business Engaged in the leasing of real estate properties    
Operating Location R.O.C.    
Percentages of ownership held by the Group 27.31% 27.31%  
Deca Technologies Inc. [member]      
Disclosure of associates and joint ventures [line items]      
Main Business Holding company and the group engaged in manufacturing, development and marketing of wafer level packaging and interconnect technology    
Operating Location British Cayman Islands    
Percentages of ownership held by the Group 17.85% 22.02%  
Cost [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land $ 12,635,388 $ 12,105,654 449,978
Cost [member] | Yann Yuan Investment Co., Ltd. [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land 6,670,035 3,934,190 237,537
Cost [member] | ChipMOS Technologies Inc. [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land 2,406,843 4,370,075 85,714
Cost [member] | M-Universe Investments Pte. Ltd. [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land 1,848,588 1,814,699 65,833
Cost [member] | Hung Ching Development & Construction Co. [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land 1,352,760 1,380,162 48,175
Cost [member] | Hung Ching Kwan Co. [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land 270,087 283,105 9,618
Cost [member] | Deca Technologies Inc. [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates before deferred gain on transfer of land 87,075 323,423 3,101
Deferred gain on transfer of land [member]      
Disclosure of associates and joint ventures [line items]      
Investments in associates $ 300,149 $ 300,149 $ 10,689