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Equity - Summary of Share Capital (Detail) shares in Thousands, $ in Thousands, $ in Thousands | Dec. 31, 2018 USD ($) shares | Dec. 31, 2018 TWD ($) shares | Dec. 31, 2017 TWD ($) shares
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Disclosure of classes of share capital [abstract] |  |  |
Numbers of shares authorized (in thousands) | 5,000,000 | 5,000,000 | 10,000,000
Numbers of shares reserved (in thousands) Employee share options | 400,000 | 400,000 | 800,000
Number of shares issued and fully paid (in thousands) | 4,321,714 | 4,321,714 | 8,738,079
Share capital authorized | $ 1,633,453 | $ 50,000,000 | $ 100,000,000
Share capital reserved Employee share options | 130,676 | 4,000,000 | 8,000,000
Share capital issued and fully paid | $ 1,411,864 | $ 43,217,144 | $ 87,380,787

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