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Investments Accounted for Using the Equity Method - Additional Information (Detail)
$ / shares in Units, $ in Thousands, $ in Thousands
 1 Months Ended 12 Months Ended
Nov. 30, 2016
TWD ($)
shares
Jul. 31, 2016
TWD ($)
shares
Jul. 31, 2016
USD ($)
$ / shares
shares
Dec. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
TWD ($)
ASE Test, Inc. [member]            
Disclosure of Investments Accounted for Using Equity Method [line Items]            
Percentage of ownership       100.00% 100.00%  
ASE Test, Inc. [member] | Advanced Microelectronic Products Inc. [member]            
Disclosure of Investments Accounted for Using Equity Method [line Items]            
Preferred shares acquired | shares 90,000,000          
Consideration paid in cash for shares | $ $ 225,000          
Advanced Microelectronic Products Inc. [member]            
Disclosure of Investments Accounted for Using Equity Method [line Items]            
Percentage of ownership 38.76%          
ASE Embedded Electronics Inc. [member]            
Disclosure of Investments Accounted for Using Equity Method [line Items]            
Increase in capital | $           $ 146,903
Percentage of ownership interest in joint venture       51.00% 51.00%  
Deca Technologies Inc. [member]            
Disclosure of Investments Accounted for Using Equity Method [line Items]            
Preferred shares acquired | shares   98,490,000 98,490,000      
Preferred shares issued per share | $ / shares     $ 0.608      
Consideration paid in cash for shares   $ 1,934,062 $ 59,882      
Percentage of ownership interest in associate   22.07% 22.07% 22.04% 22.07%