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Income Tax Expense - Details of Deferred Tax Assets (Liabilities) (Detail) $ in Thousands, $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2020 TWD ($) | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2017 TWD ($)
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Recognized in profit or loss | $ 14,237 | $ (35,367) | $ (98,667) |  |
Deferred tax assets | 185,691 | 194,552 | 226,716 | $ 6,613 | $ 212,372
Deferred tax liabilities | (310,427) | (309,129) | (308,759) | $ (11,055) | $ (174,293)
Deferred tax assets unrealized loss on inventories [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 12,700 | 7,232 | 9,132 |  |
Effects on initial application of IFRS 9 and IFRS 15 |  |  | (770) |  |
Recognized in profit or loss | 3,263 | 5,468 | (1,130) |  |
Ending balance | 15,963 | 12,700 | 7,232 |  |
Property, plant and equipment, deferred tax assets [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 38,668 | 64,183 | 55,494 |  |
Recognized in profit or loss | (2,267) | (25,515) | 8,689 |  |
Ending balance | 36,401 | 38,668 | 64,183 |  |
Provisions [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 5,600 | 12,396 | 21,643 |  |
Recognized in profit or loss | (2,922) | (6,796) | (9,247) |  |
Ending balance | 2,678 | 5,600 | 12,396 |  |
Deferred tax assets deferred revenue [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 27,650 | 34,156 | 39,485 |  |
Recognized in profit or loss | (6,506) | (6,506) | (5,329) |  |
Ending balance | 21,144 | 27,650 | 34,156 |  |
Net defined benefit liability [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 92,612 | 100,743 | 78,451 |  |
Recognized in profit or loss | (4,089) | (3,948) | 7,889 |  |
Recognized in other comprehensive income | 10,398 | (4,183) | 14,403 |  |
Ending balance | 98,921 | 92,612 | 100,743 |  |
Unrealized exchange losses deferred tax assets [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 17,296 | 3,575 | 8,167 |  |
Effects on initial application of IFRS 9 and IFRS 15 |  |  | 144 |  |
Recognized in profit or loss | (7,381) | 13,721 | (4,736) |  |
Ending balance | 9,915 | 17,296 | 3,575 |  |
Investment tax credit [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance |  | 4,420 |  |  |
Recognized in profit or loss |  | (4,420) | 4,420 |  |
Ending balance |  |  | 4,420 |  |
Other [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 26 | 11 |  |  |
Recognized in profit or loss | 643 | 15 | 11 |  |
Ending balance | 669 | 26 | 11 |  |
Deferred tax asset [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | 194,552 | 226,716 | 212,372 |  |
Effects on initial application of IFRS 9 and IFRS 15 |  |  | (626) |  |
Recognized in profit or loss | (19,259) | (27,981) | 567 |  |
Recognized in other comprehensive income | 10,398 | (4,183) | 14,403 |  |
Ending balance | 185,691 | 194,552 | 226,716 |  |
Property, plant and equipment, deferred tax liabilities [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | (288,980) | (281,594) | (174,293) |  |
Recognized in profit or loss | 33,496 | (7,386) | (107,301) |  |
Ending balance | (255,484) | (288,980) | (281,594) |  |
Deferred tax liabilities, contract assets [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Effects on initial application of IFRS 9 and IFRS 15 |  |  | (8,067) |  |
Recognized in profit or loss |  |  | 8,067 |  |
Financial assets at fair value through other comprehensive income [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | (20,149) | (27,165) |  |  |
Effects on initial application of IFRS 9 and IFRS 15 |  |  | (8,636) |  |
Recognized in other comprehensive income | (34,794) | 7,016 | (18,529) |  |
Ending balance | (54,943) | (20,149) | (27,165) |  |
Deferred tax liabilities [member] |  |  |  |  |
Disclosure of the detail of deferred tax assets and liabilities [line items] |  |  |  |  |
Beginning balance | (309,129) | (308,759) | (174,293) |  |
Effects on initial application of IFRS 9 and IFRS 15 |  |  | (16,703) |  |
Recognized in profit or loss | 33,496 | (7,386) | (99,234) |  |
Recognized in other comprehensive income | (34,794) | 7,016 | (18,529) |  |
Ending balance | $ (310,427) | $ (309,129) | $ (308,759) |  |

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