Income Tax Expense - Reconciliation of Income Tax Expense and Accounting Profit Before Income Tax (Detail) $ in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2024 TWD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 TWD ($)	Dec. 31, 2022 TWD ($)
Reconciliation of income tax expense and accounting profit before income tax [abstract]
Tax calculated based on profit before tax and statutory tax rate	$ 338,116		$ 451,676	$ 804,086
Effects from adjustments based on regulation	(38,880)		(74,094)	(131,873)
Gain (loss) on investment in associates	(31,151)		19,228	11,923
Prior year income tax overestimation	(127,768)		(182,778)	(255,935)
Income tax on unappropriated retained earnings	66,066		85,607	159,744
Effect of different tax rates in countries in which the Group operates	1,134		1,022	230
Income tax expense	$ 207,517	$ 6,328	$ 300,661	$ 588,175

Adjustments of tax expense (income) recognised in the period for current tax of prior periods.

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The aggregate amount included in the determination of profit (loss) for the period in respect of current tax and deferred tax. [Refer: Current tax expense (income); Deferred tax expense (income)]

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The amount that represents the difference between the tax expense (income) and the product of the accounting profit multiplied by the applicable tax rate(s) that relates to foreign tax rates. [Refer: Accounting profit]

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The product of the accounting profit multiplied by the applicable tax rate(s). [Refer: Accounting profit; Applicable tax rate]

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Effect of adjustments based on regulation.

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Reconciliation of income tax expense and accounting profit before income tax.

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Tax effect of additional income tax on unappropriated earnings.

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Tax effect of gain loss on investments in associates.

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