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Other equity interest - Summary of Other Equity Interest (Detail) $ in Thousands, $ in Thousands | 12 Months Ended
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Dec. 31, 2020 TWD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 TWD ($) | Dec. 31, 2018 TWD ($)
Disclosure of Other Equity Interest [Line Items] |  |  |  |
Ending balance | $ 19,802 | $ 705 |  |
Financial statements translation differences of foreign operations [member] |  |  |  |
Disclosure of Other Equity Interest [Line Items] |  |  |  |
Beginning balance | (89,682) |  | $ 14,516 | $ 65,593
Adjust Balance on Other Equity Interest |  |  |  | 65,593
Currency translation differences - The company | 28,352 |  | (104,198) | (51,077)
Ending balance | (61,330) |  | (89,682) | 14,516
Unrealized gain (loss) on valuation of financial assets at fair value through other comprehensive income [member] |  |  |  |
Disclosure of Other Equity Interest [Line Items] |  |  |  |
Beginning balance | 66,386 |  | 106,898 |
Effect on initial application of IFRS 9 |  |  |  | 42,843
Adjust Balance on Other Equity Interest |  |  |  | 42,843
Evaluation adjustment - The Company | 140,199 |  | (52,549) | 85,022
Evaluation adjustment - Associates | 22,925 |  | 5,093 | (2,438)
Evaluation adjustment related tax - The Company | (34,794) |  | 7,016 | (18,529)
Disposal of investment accounted for using equity method |  |  | (72) |
Ending balance | 194,716 |  | 66,386 | 106,898
Unrealized gain on valuation of available -for-sale financial assets [member] |  |  |  |
Disclosure of Other Equity Interest [Line Items] |  |  |  |
Beginning balance |  |  |  | 678
Effect on initial application of IFRS 9 |  |  |  | (678)
Unearned employee awards [member] |  |  |  |
Disclosure of Other Equity Interest [Line Items] |  |  |  |
Beginning balance |  |  | (1,701) | (54,570)
Effect on initial application of IFRS 9 |  |  |  | 0
Adjust Balance on Other Equity Interest |  |  |  | (54,570)
Employee restricted shares - The company |  |  | 1,701 | 52,869
Ending balance |  |  |  | (1,701)
Other reserves [member] |  |  |  |
Disclosure of Other Equity Interest [Line Items] |  |  |  |
Beginning balance | (23,296) |  | 119,713 | 11,701
Effect on initial application of IFRS 9 |  |  |  | 42,165
Adjust Balance on Other Equity Interest |  |  |  | 53,866
Currency translation differences - The company | 28,352 |  | (104,198) | (51,077)
Employee restricted shares - The company | 140,199 |  | 1,701 | 52,869
Evaluation adjustment - The Company |  |  | (52,549) | 85,022
Evaluation adjustment - Associates | 22,925 |  | 5,093 | (2,438)
Evaluation adjustment related tax - The Company | (34,794) |  | 7,016 | (18,529)
Disposal of investment accounted for using equity method |  |  | (72) |
Ending balance | $ 133,386 |  | $ (23,296) | $ 119,713

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- Definition A component of equity representing reserves within equity, not including retained earnings. [Refer: Retained earnings] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 78 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_78_e&doctype=Standard -URIDate 2020-01-01 + Details
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