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Share-based Payment Arrangements - Summary of Information About ASE Mauritius Inc. Option Plan (Detail) - ASE Mauritius Inc. option plan [member]
shares in Thousands, pure in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]      
Number of options, beginning balance | shares 28,470 28,470 28,545
Number of options, forfeited | shares (250)   (75)
Number of options, Expired (28,220)    
Number of options, ending balance | shares   28,470 28,470
Number of options, exercisable, end of year | shares   28,470 28,470
Weighted average exercise price, Beginning balance $ 1.7 $ 1.7 $ 1.7
Weighted average exercise price, Options forfeited 1.7   1.7
Weighted average exercise price, Options expired $ 1.7    
Weighted average exercise price, Ending balance   1.7 1.7
Weighted average exercise price, Options exercisable, end of year   $ 1.7 $ 1.7