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Trade Receivables, Net - Summary of Movement of Allowance for Doubtful Trade Receivables (Detail) - Trade receivables [member]
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2015
TWD ($)
Disclosure of financial assets [Line Items]        
Beginning balance $ 53,709 $ 1,812 $ 82,906 $ 84,145
Impairment losses recognized 13,629 460 (28,022) 8,232
Amount written off (34) (1)   (7,826)
Effect of foreign currency exchange differences (2,403) (81) (1,175) (1,645)
Ending balance 64,901 2,190 53,709 82,906
Impaired individually [member]        
Disclosure of financial assets [Line Items]        
Beginning balance 16,453 555 39,046 28,305
Impairment losses recognized 9,527 322 (21,501) 18,816
Amount written off       (7,617)
Effect of foreign currency exchange differences (850) (29) (1,092) (458)
Ending balance 25,130 848 16,453 39,046
Impaired collectively [member]        
Disclosure of financial assets [Line Items]        
Beginning balance 37,256 1,257 43,860 55,840
Impairment losses recognized 4,102 138 (6,521) (10,584)
Amount written off (34) (1)   (209)
Effect of foreign currency exchange differences (1,553) (52) (83) (1,187)
Ending balance $ 39,771 $ 1,342 $ 37,256 $ 43,860