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Earnings Per Share - Summary of Earnings and Weighted Average Number of Ordinary Shares Outstanding in Computation of Earnings Per Share (Detail) shares in Thousands, $ in Thousands, $ in Thousands | 12 Months Ended
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Dec. 31, 2018 USD ($) shares | Dec. 31, 2018 TWD ($) shares | Dec. 31, 2017 TWD ($) shares | Dec. 31, 2016 TWD ($) shares
Earnings per share [line items] |  |  |  |
Profit for the year attributable to owners of the Company | $ 856,606 | $ 26,220,721 | $ 22,819,119 | $ 21,324,423
Effect of potentially dilutive ordinary shares: |  |  |  |
From subsidiaries | (13,665) | (418,295) | (813,627) | (374,359)
From the investments in associates | $ |  |  | (367,687) | (494,388)
From convertible bonds | $ |  |  | 93,781 | (1,165,506)
Earnings used in the computation of diluted earnings per share | $ 842,941 | $ 25,802,426 | $ 21,731,586 | $ 19,290,170
Weighted average number of ordinary shares in the computation of basic earnings per share | 4,245,247 | 4,245,247 | 4,080,443 | 3,831,435
Effect of potentially dilutive ordinary shares: |  |  |  |
From convertible bonds |  |  | 62,456 | 257,648
From employee share options | 5,103 | 5,103 | 19,934 | 29,609
From employees' compensation | 779 | 779 | 21,787 | 23,373
Weighted average number of ordinary shares in computation of diluted earnings per share | 4,251,129 | 4,251,129 | 4,184,620 | 4,142,065
Before Retrospectively Adjusted [member] |  |  |  |
Effect of potentially dilutive ordinary shares: |  |  |  |
Weighted average number of ordinary shares in the computation of basic earnings per share |  |  | 8,160,887 | 7,662,870
Effect of potentially dilutive ordinary shares: |  |  |  |
From convertible bonds |  |  | 124,911 | 515,295
From employee share options |  |  | 39,868 | 59,218
From employees' compensation |  |  | 43,574 | 46,746
Weighted average number of ordinary shares in computation of diluted earnings per share |  |  | 8,369,240 | 8,284,129

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