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Investments Accounted for Using the Equity Method - Summary of Investments in joint ventures Accounted for using the Equity Method (Detail) $ in Thousands, $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2019 USD ($)
Disclosure of joint ventures [line items] |  |  |
Carrying Amount | $ 279,702 | $ 180,494 | $ 9,351
ASE Embedded Electronics Inc. [member] |  |  |
Disclosure of joint ventures [line items] |  |  |
Main Business | Engaged in the production of embedded substrate |  |
Operating Location | R.O.C. |  |
Carrying Amount |  | $ 180,494 |
percentages of ownership |  | 51.00% |
SUMA-USI Electronics Co., Ltd [member] |  |  |
Disclosure of joint ventures [line items] |  |  |
Main Business | Engaged in the design and production of electronic products |  |
Operating Location | China |  |
Carrying Amount | $ 279,702 |  | $ 9,351
percentages of ownership | 49.00% |  |

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