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Financial Assets at Fair Value Through Other Comprehensive Income - Additional Information (Detail)
Bonds in Thousands, $ in Thousands, $ in Thousands
 1 Months Ended
Jun. 30, 2016
TWD ($)
Bonds
Dec. 31, 2018
USD ($)
Dec. 31, 2018
TWD ($)
Dec. 31, 2017
TWD ($)
Financial assets at fair value through other comprehensive income [line items]        
Unsecured subordinate corporate bonds amount   $ 247,754 $ 7,583,761 $ 1,642,840
Unsecured subordinate corporate bonds [member]        
Financial assets at fair value through other comprehensive income [line items]        
Unsecured subordinate corporate bonds amount | $ $ 1,000,000     $ 1,000,000
Number of bonds acquired | Bonds 1,000      
Corporate bonds annual interest rate 3.50%      
Effective interest rate   3.20% 3.20% 3.20%