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Goodwill - Summary of Carrying Amounts of Goodwill Allocated to Cash-generating Units (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 TWD ($) | Dec. 31, 2016 TWD ($)
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Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | $ 50,198,436 | $ 1,678,316 | $ 49,974,446 | $ 1,670,827 | $ 9,934,494 | $ 10,490,309
Packaging segment [member] |  |  |  |  |  |
Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | 35,717,828 | 1,194,177 | 35,729,371 |  |  |
Testing segment [member] |  |  |  |  |  |
Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | 13,421,321 | 448,724 | 13,448,886 |  |  |
All other segments [member] |  |  |  |  |  |
Disclosure of information for cash-generating units [line items] |  |  |  |  |  |
Goodwill | $ 1,059,287 | $ 35,415 | $ 796,189 |  |  |

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