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Operating Segments Information - Summary of Revenue from Major Products and Services (Detail)
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2020
TWD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
TWD ($)
Dec. 31, 2018
TWD ($)
Disclosure of products and services [line items]        
Operating revenue $ 476,978,710 $ 16,986,421 $ 413,182,184 $ 371,092,421
Packaging service [member]        
Disclosure of products and services [line items]        
Operating revenue 218,666,071 7,787,253 198,916,897 178,308,222
Testing service [member]        
Disclosure of products and services [line items]        
Operating revenue 47,271,074 1,683,443 42,658,686 35,903,202
EMS        
Disclosure of products and services [line items]        
Operating revenue 204,690,669 7,289,554 165,789,479 151,890,384
Other products and services [member]        
Disclosure of products and services [line items]        
Operating revenue $ 6,350,896 $ 226,171 $ 5,817,122 $ 4,990,613