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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% |

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