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Goodwill - Summary of Goodwill (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 reconciliation of changes in goodwill [line items]        
Beginning balance $ 50,198,436 $ 1,787,693 $ 49,974,446 $ 9,934,494
Acquisition through business combinations 4,625,269 164,718 264,977 39,990,231
Effect of foreign currency exchange differences (46,266) (1,647) (40,987) 49,721
Ending balance 54,777,439 1,950,764 50,198,436 49,974,446
Cost [member]        
Disclosure of reconciliation of changes in goodwill [line items]        
Beginning balance 52,612,549 1,873,666 52,388,559 12,348,607
Acquisition through business combinations 4,625,269 164,718 264,977 39,990,231
Effect of foreign currency exchange differences (46,266) (1,647) (40,987) 49,721
Ending balance 57,191,552 2,036,737 52,612,549 52,388,559
Accumulated impairment [Member]        
Disclosure of reconciliation of changes in goodwill [line items]        
Beginning balance 2,414,113 85,973 2,414,113 2,414,113
Acquisition through business combinations 0 0    
Effect of foreign currency exchange differences 0 0    
Ending balance $ 2,414,113 $ 85,973 $ 2,414,113 $ 2,414,113