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Significant Contingent Liabilities and Unrecognized Commitments - Additional Information (Detail)
$ in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Dec. 31, 2013
TWD ($)
Jan. 31, 2018
TWD ($)
Jan. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Disclosure of contingent liabilities [line items]              
Unused letters of credit $ 20,000   $ 97,000       $ 675
Committed to purchase property, plant and equipment 7,019,377   6,630,957       $ 236,821
Prepayment of property, plant and equipment 294,194 $ 9,926 668,509        
Construction contract related to real estate business $ 1,548,806 $ 52,254 $ 1,574,822        
Subsequent Event [Member]              
Disclosure of contingent liabilities [line items]              
Contribution to be made for environmental protection         $ 100,000 $ 3,374  
Taiwan [member]              
Disclosure of contingent liabilities [line items]              
Contractual period for environmental protection       30 years      
Contribution to be made for environmental protection       $ 3,000,000