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Equity - Summary of Capital Surplus (Detail) $ in Thousands, $ in Thousands | Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($)
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Disclosure of classes of share capital [abstract] |  |  |
Issuance of ordinary shares | $ 13,070,330 | $ 436,989 | $ 12,906,401
Merger by share exchange | 117,693,658 | 3,934,927 | 117,693,658
Difference between consideration and the carrying amount of the subsidiaries' net assets during actual disposal or acquisition | 3,254,489 | 108,809 | 6,034,102
Capital surplus deficit distributed as cash dividends | 134,018,477 | 4,480,725 | 136,634,161
Changes in percentage of ownership interest in subsidiaries | 891,876 | 29,819 | 3,727,336
Treasury share transactions | 364,708 | 12,193 | 182,354
Exercised employee share options | 1,443,995 | 48,278 | 1,366,480
Expired share options (Notes 22 and 29) | 645,903 | 21,595 | 645,978
Share of changes in capital surplus of associates | 16,266 | 544 | 87,136
Dividends that the claim period has elapsed and unclaimed by shareholders | 1,942 | 65 | 872
Capital surplus offset deficit | 3,364,690 | 112,494 | 6,010,156
Employee share options | 1,304,250 | 43,606 | 583,542
Others | 222,946 | 7,454 | 48,805
Capital surplus for other purpose | 1,527,196 | 51,060 | 632,347
Capital surplus | $ 138,910,363 | $ 4,644,279 | $ 143,276,664

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