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Income Tax - Summary of Income Tax Recognized in Other Comprehensive Income (Detail)
$ in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Income tax relating to components of other comprehensive income [abstract]        
Deferred income tax related to remeasurement of defined benefit plans $ (51,217) $ (1,728) $ 73,637 $ 11,002