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Issued Capital - Additional Information (Detail) $ / shares in Units, $ in Thousands, $ in Thousands |  | 12 Months Ended |
--- | --- | --- | ---
Aug. 15, 2018 TWD ($) shares | Dec. 31, 2019 TWD ($) $ / shares shares | Dec. 31, 2018 TWD ($) shares | Dec. 31, 2017 shares | Dec. 31, 2019 USD ($) shares
Disclosure of classes of share capital [line items] |  |  |  |  |
Ordinary shares par value | $ / shares |  | $ 10 |  |  |
Number of shares outstanding |  | 727,240 |  |  | 727,240
Percentage of capital reduction | 15.00% |  |  |  |
Amount of capital reduction | $ | $ 1,329,446 |  |  |  |
Capital reduction |  |  |  | 0 |
Authorised capital | $ |  | $ 9,700,000 |  |  |
Number of shares authorised |  | 970,000 |  |  | 970,000
Paid in capital |  | $ 7,272,401 | $ 7,528,577 |  | $ 243,143
Ordinary shares [member] |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Number of shares outstanding |  | 96,035 |  |  | 96,035
Capital reduction | 132,945,000 |  | (128,422,000) |  |
American depositary shares [member] |  |  |  |  |
Disclosure of classes of share capital [line items] |  |  |  |  |
Number of shares represented by each unit of ADS |  | 20 |  |  |
Number of shares outstanding |  | 4,801,737 |  |  | 4,801,737

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