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Financial Risk Management and Fair Values of Financial Instruments - Summary of Natures of Assets and Liabilities (Detail) - TWD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through profit or loss $ 63,488 $ 11,038
Financial assets at fair value 325,495 132,846
Foreign partnership interest [member] | Recurring fair value measurement [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through profit or loss 10,368 11,038
Foreign unlisted stocks [member] | Recurring fair value measurement [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through other comprehensive income 262,007 121,808
Listed stocks [member] | Recurring fair value measurement [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through profit or loss 53,120  
Level 1 [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value 53,120  
Level 1 [member] | Listed stocks [member] | Recurring fair value measurement [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through profit or loss 53,120  
Level 3 [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value 272,375 132,846
Level 3 [member] | Foreign partnership interest [member] | Recurring fair value measurement [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through profit or loss 10,368 11,038
Level 3 [member] | Foreign unlisted stocks [member] | Recurring fair value measurement [member]    
Disclosure of detailed information about financial instruments [Line Items]    
Financial assets at fair value through other comprehensive income $ 262,007 $ 121,808