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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
Aug. 31, 2018
USD ($)
shares
Apr. 29, 2018
$ / shares
Apr. 29, 2018
$ / shares
Dec. 31, 2018
USD ($)
yr
$ / shares
Dec. 31, 2018
USD ($)
yr
$ / shares
Dec. 31, 2018
USD ($)
yr
shares
Dec. 31, 2018
TWD ($)
shares
Dec. 31, 2017
TWD ($)
yr
$ / shares
Dec. 31, 2016
TWD ($)
$ / shares
shares
Dec. 31, 2007
shares
Dec. 31, 2018
TWD ($)
yr
Aug. 31, 2018
TWD ($)
Disclosure of terms and conditions of share-based payment arrangement [Line Items]                        
Capital surplus decreased $ 311                     $ 9,530
Compensation cost of employee share options           $ 7,045 $ 215,648 $ 354,765 $ 470,788      
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 | shares                   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       $ 40,492 $ 40,492 $ 40,492   $ 52,388     $ 1,239,456  
USISH 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          
Remaining contractual life of share options | yr       6.9 6.9 6.9   7.9     6.9  
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          
Number of employee share option plans           5 5          
Share option to purchase of ordinary shares | shares           0.5 0.5          
Weighted average exercise price of share options | (per share)   $ 41.0 $ 1.3         $ 37.6 $ 36.2      
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 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 | shares                 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 | 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)       $ 68.5 $ 2.2