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Share-based Payment Arrangements - Additional Information (Detail)
$ / shares in Units, $ / shares in Units, $ in Thousands, $ in Thousands
 1 Months Ended 4 Months Ended 8 Months Ended 12 Months Ended
Nov. 30, 2019
shares
Dec. 31, 2018
TWD ($)
$ / shares
Aug. 31, 2018
TWD ($)
shares
Apr. 29, 2018
$ / shares
Dec. 31, 2018
TWD ($)
shares
Dec. 31, 2019
TWD ($)
shares
$ / shares
Dec. 31, 2019
USD ($)
shares
$ / shares
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
TWD ($)
shares
$ / shares
Dec. 31, 2016
TWD ($)
shares
Dec. 31, 2007
shares
Dec. 31, 2019
USD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Capital surplus decreased | $     $ 9,530                  
Compensation cost of employee share options           $ 871,699 $ 29,144 $ 215,648 $ 354,765      
ASE Mauritius Inc. option plan [member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Valid term of share option plans           10 years 10 years          
Number of shares granted                     30,000,000  
Reclassification from non-controlling interest to capital surplus arising from expired employee share options | $           $ 159,200            
USIE option plans [member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Capital surplus decreased   $ 1,239,456     $ 1,239,456 $ 981,078   $ 1,239,456 $ 52,388     $ 32,801
USISH option plans [member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Valid term of share option plans 5 years         10 years 10 years          
Capital surplus decreased           $ 105,785           $ 3,537
Options granted           23,323,000 23,323,000          
USISH option plans [member] | Share Option [Member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Options granted 17,167,000                      
ASE Inc. option plans [member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Valid term of share option plans           10 years 10 years          
Share option to purchase of ordinary shares           0.5 0.5          
Weighted average exercise price of share options | $ / shares   $ 68.5   $ 41.0         $ 37.6      
Reclassification from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $                 $ 47,087      
New shares reserved for subscription by employees under cash capital increase [member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Options granted                 30,000,000      
Options granted to employees to purchase newly issued shares, percentage                   10.00%    
Employee benefits expense and capital surplus arising from exercised employee share option | $                   $ 84,000    
Number of shares has not been exercised                   4,836,000    
Amount reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options | $                   $ 13,541    
The Company Option Plans [member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Number of shares registered shares     150,000,000                  
Valid term of share option plans           10 years 10 years          
Percentage of cash dividend per ordinary share exceeds market price           1.50% 1.50%          
Weighted average exercise price of share options | (per share)           $ 69.3 $ 2.3          
Options granted         131,863,000              
USISH core employees stock ownership plan [Member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Options granted 6,156,000                      
USISH core employees stock ownership plan [Member] | Phase One [Member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Valid term of share option plans 4.5 years                      
USISH core employees stock ownership plan [Member] | Phase Two [Member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Valid term of share option plans 3.5 years                      
USISH core employees stock ownership plan [Member] | Phase Three [Member]                        
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Valid term of share option plans 2.5 years