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Financial Risk Management And Fair Values Of Financial Instruments - Summary of Effect of Profit or Loss or of Other Comprehensive Income from Financial Assets Categorized (Detail) - Financial instruments at fair value through other comprehensive income [member] - TWD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items] |  |
Favorable Changes | $ 2,363 | $ 3,725
Unfavorable Changes In Fair Value | 2,413 | 3,630
Enter prise value EBITDA multiple [member] |  |
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items] |  |
Favorable Changes | 850 | 1,563
Unfavorable Changes In Fair Value | 900 | 1,512
Discount for lack of marketability [member] |  |
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items] |  |
Favorable Changes | 1,460 | 2,093
Unfavorable Changes In Fair Value | 1,460 | 2,050
Foreign unlisted stocks [member] | Price to book ratio multiple [member] |  |
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items] |  |
Favorable Changes | 53 | 69
Unfavorable Changes In Fair Value | $ 53 | $ 68

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