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Equity - Additional Information (Detail)
$ / shares in Units, $ in Thousands, $ in Thousands
 1 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2018
TWD ($)
Dec. 31, 2018
$ / shares
shares
Dec. 31, 2017
shares
Oct. 13, 2017
shares
Jul. 13, 2017
shares
Disclosure of classes of share capital [line items]            
Share price | $ / shares     $ 10      
Shares included in authorized shares not yet completed share registration process       500,000,000    
Number of ordinary shares issued         323,094,000 101,164,000
Number of shares represented by each ADS     2 2    
Distribution of cash from capital surplus arising from issuance of ordinary shares $ 352,695 $ 10,795,980        
Percentage of legal reserve     10.00%      
Percentage of legal reserve on share capital     25.00%      
American depository shares (ADs) [member]            
Disclosure of classes of share capital [line items]            
Number of shares represented by each ADS     2      
Number of shares outstanding     140,042,000 115,261,000    
Ordinary shares [member]            
Disclosure of classes of share capital [line items]            
Number of shares outstanding     280,085,000 576,305,000    
Cash capital increase [member]            
Disclosure of classes of share capital [line items]            
Share price | $ / shares     $ 34.3      
Number of ordinary shares issued     300,000,000      
A.S.E. Holding Limited [member]            
Disclosure of classes of share capital [line items]            
Proportion of ownership interest in subsidiary     100.00% 100.00%    
Number of ordinary shares exchanged from ASE Holding     0.5      
Repurchase of ordinary shares     1,852,000      
Repurchase of ordinary shares, price per share | $ / shares     $ 38.5      
Treasury shares canceled     121,852,000      
Converted bonds [member]            
Disclosure of classes of share capital [line items]            
Ordinary shares issued under conversion of Bonds     424,258,000      
Top of range [member]            
Disclosure of classes of share capital [line items]            
Percentage of cash dividend on dividend distribution     30.00%