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Operating Segments Information - Summary of Geographical Information (Detail)
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2020
USD ($)
Disclosure of geographical areas [line items]          
Operating revenue $ 476,978,710 $ 16,986,421 $ 413,182,184 $ 371,092,421  
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets 337,369,625   334,926,069   $ 12,014,588
United States [Member]          
Disclosure of geographical areas [line items]          
Operating revenue 297,117,001 10,581,090 245,521,027 230,791,164  
Taiwan [member]          
Disclosure of geographical areas [line items]          
Operating revenue 64,829,301 2,308,736 51,244,470 45,630,792  
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets 239,353,978   239,532,971   8,524,002
Asia [Member]          
Disclosure of geographical areas [line items]          
Operating revenue 74,447,091 2,651,249 75,938,364 56,031,108  
Europe [Member]          
Disclosure of geographical areas [line items]          
Operating revenue 39,477,306 1,405,887 38,613,132 36,844,258  
Other geographical areas [member]          
Disclosure of geographical areas [line items]          
Operating revenue 1,108,011 $ 39,459 1,865,191 $ 1,795,099  
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets 34,107,657   26,645,450   1,214,660
China [member]          
Disclosure of geographical areas [line items]          
Noncurrent assets, excluding financial instruments, post-employment benefit assets and deferred tax assets $ 63,907,990   $ 68,747,648   $ 2,275,926