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Segment Information - Schedule of Geographical Information (Detail) - TWD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Non-current assets [abstract] |  |
Total non-current assets | $ 18,733,638 | $ 16,848,181
ROC [member] |  |
Non-current assets [abstract] |  |
Total non-current assets | 18,727,979 | 16,847,172
Others [Member] |  |
Non-current assets [abstract] |  |
Total non-current assets | $ 5,659 | $ 1,009

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