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Property, Plant and Equipment - Summary of maturity analysis of operating lease payments receivable (Detail) - Operating Lease Agreement [Member]
$ in Millions
Dec. 31, 2019
TWD ($)
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]  
Operating Lease Payment Receivables $ 52.4
Year 1 [member]  
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]  
Operating Lease Payment Receivables 18.4
Year 2 [Member]  
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]  
Operating Lease Payment Receivables 17.0
Year 3 [member]  
Disclosure Of Maturity Analysis Of Operating Lease Receivables [Line Items]  
Operating Lease Payment Receivables $ 17.0