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Financial Risk Management and Fair Values of Financial Instruments - Summary of Movements of Level 3 (Detail) - TWD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Disclosure of detailed information about financial instruments [Line Items] |  |
Movement of financial instruments beginning balance | $ 185,828 |
Effects on initial application of IFRS 9 |  | $ 100,768
Gains or losses recognized in profit or loss Recorded as non-operating income (expenses) | (433) | 38
Gains or losses recognized in other comprehensive income (losses) Recorded as unrealized gains on valuation of financial assets at fair value through other comprehensive income | (52,549) | 85,022
Movement of financial instruments ending balance | 132,846 | 185,828
Debt instruments [member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Movement of financial instruments beginning balance | 11,471 |
Effects on initial application of IFRS 9 |  | 11,433
Gains or losses recognized in profit or loss Recorded as non-operating income (expenses) | (433) | 38
Movement of financial instruments ending balance | 11,038 | 11,471
Equity instruments [member] |  |
Disclosure of detailed information about financial instruments [Line Items] |  |
Movement of financial instruments beginning balance | 174,357 |
Effects on initial application of IFRS 9 |  | 89,335
Gains or losses recognized in other comprehensive income (losses) Recorded as unrealized gains on valuation of financial assets at fair value through other comprehensive income | (52,549) | 85,022
Movement of financial instruments ending balance | $ 121,808 | $ 174,357

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