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Equity - Summary of Unrealized Gain (Loss) on Available-for-sale Financial Assets (Detail) $ in Thousands, $ in Thousands | 12 Months Ended
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Dec. 31, 2019 TWD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 TWD ($) | Dec. 31, 2017 TWD ($)
Balance at January 1 | $ 219,027,922 |  | $ 201,310,187 | $ 166,841,165
Unrealized gain arising on revaluation of available-for-sale financial assets |  |  |  | 224,036
Share from associates and joint venture accounted for using the equity method | (85,975) | $ (2,874) | 136,608 | 264,389
Balance at December 31 | $ 212,802,312 | $ 7,114,755 | 219,027,922 | 201,310,187
Reserve of gains and losses on remeasuring available-for-sale financial assets excluding changes in capital surplus [member] |  |  |  |
Balance at January 1 |  |  | $ 422,570 | (197,314)
Unrealized gain arising on revaluation of available-for-sale financial assets |  |  |  | 169,585
Cumulative loss reclassified to profit or loss on impairment of available-for-sale financial assets |  |  |  | 50,206
Cumulative gain reclassified to profit or loss on disposal of available-for-sale financial assets |  |  |  | (1,517)
Share from associates and joint venture accounted for using the equity method |  |  |  | 401,610
Balance at December 31 |  |  |  | $ 422,570

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