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Income Tax Expense - Deferred Tax Charged to Other Comprehensive Income (Detail) $ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 TWD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 TWD ($)	Dec. 31, 2018 TWD ($)
Income tax relating to components of other comprehensive income [abstract]
Unrealized gain (loss) on valuation of financial assets at fair value through other comprehensive income	$ 34,794		$ (7,016)	$ 17,005
Remeasurement of defined benefit obligations	(10,398)		4,183	(11,992)
Impact of change in tax rate				(887)
Total	$ 24,396	$ 869	$ (2,833)	$ 4,126

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- References

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- Definition

The amount of income tax relating to amounts recognised in other comprehensive income that will not be reclassified to profit or loss. [Refer: Income tax relating to components of other comprehensive income]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of income tax relating to amounts recognised in other comprehensive income in relation to financial assets measured at fair value through other comprehensive income. [Refer: Financial assets measured at fair value through other comprehensive income; Other comprehensive income]

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- Definition

The amount of income tax relating to amounts recognised in other comprehensive income in relation to remeasurements of defined benefit plans. [Refer: Other comprehensive income; Reserve of remeasurements of defined benefit plans; Defined benefit plans [member]]

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- Definition

Income tax relating to impact of change in tax rate included in other comprehensive income.

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