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
Dec. 31, 2020	Dec. 31, 2019
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items]
Favorable Changes	$ 5,325	$ 2,363
Unfavorable Changes In Fair Value	5,267	2,413
Enter prise value EBITDA multiple [member]
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items]
Favorable Changes	2,153	850
Unfavorable Changes In Fair Value	2,153	900
Discount for lack of marketability [member]
Disclosure of significant unobservable inputs used in fair value measurement of equity [line items]
Favorable Changes	3,142	1,460
Unfavorable Changes In Fair Value	3,084	1,460
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	30	53
Unfavorable Changes In Fair Value	$ 30	$ 53

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

Dec. 31, 2020

Dec. 31, 2019

Disclosure of significant unobservable inputs used in fair value measurement of equity [line items]

Favorable Changes

$ 5,325

$ 2,363

Unfavorable Changes In Fair Value

5,267

2,413

Enter prise value EBITDA multiple [member]

Disclosure of significant unobservable inputs used in fair value measurement of equity [line items]