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Share-based Payment Arrangements - Additional Information (Detail)
$ / shares in Units, $ / shares in Units, shares in Thousands, $ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
TWD ($)
yr
$ / shares
Dec. 31, 2017
USD ($)
$ / shares
Dec. 31, 2016
TWD ($)
yr
$ / shares
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
TWD ($)
$ / shares
Dec. 31, 2007
shares
Dec. 31, 2017
USD ($)
yr
Disclosure of terms and conditions of share-based payment arrangement [Line Items]              
Compensation cost of employee share options $ 438,765 $ 14,803 $ 470,788   $ 133,496    
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 7.9   8.9       7.9
USIE option plans [member]              
Disclosure of terms and conditions of share-based payment arrangement [Line Items]              
Capital surplus decreased $ 52,388   $ 444,320       $ 1,767
Incremental fair value granted, modified share-based payment arrangements | $         $ 13,721    
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          
Weighted average exercise price of share options | (per share) $ 37.60 $ 1.27 $ 36.20   $ 38.80    
Reclassification from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options $ 47,087 $ 1,589          
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  
Reclassification from non-controlling interest to capital surplus arising from expired employee share options $ 159,200 $ 5,371          
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% 10.00%      
Employee benefits expense and capital surplus arising from exercised employee share option     $ 84,000 $ 2,834      
Number of shares has not been exercised     4,836 4,836      
Amount reclassified from capital surplus arising from exercised employee share options to capital surplus arising from expired employee share options     $ 13,541 $ 457