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Accounts and notes receivable - Summary of Accounts and notes receivable (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Jan. 01, 2018 TWD ($)
--- | --- | --- | --- | ---
Disclosure of financial assets [Line Items] |  |  |  |
Accounts and notes receivable | $ 4,453,669 | $ 148,902 | $ 4,747,288 |
Accounts receivable [member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Accounts and notes receivable | 4,454,255 |  | 4,747,834 | $ 4,013,705
Notes receivable [member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Accounts and notes receivable | 765 |  | 1,595 |
Loss allowance [member] |  |  |  |
Disclosure of financial assets [Line Items] |  |  |  |
Accounts and notes receivable | $ (1,351) |  | $ (2,141) |

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