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Retained Earnings - Details of Retained Earnings (Detail) - TWD ($) $ / shares in Units, $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of reserves within equity [abstract] |  |  |
Legal reserve | $ 258,416 | $ 110,308 | $ 302,653
Special reserve | 19,802 |  |
Cash dividend | $ 1,309,032 | $ 872,718 | $ 256,806
Cash dividend, cash distribution per share | $ 1.80 | $ 1.20 | $ 0.30

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