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Income Tax - Tax-exemption Information Related to Profits Generated from Certain Projects (Detail)
12 Months Ended
Dec. 31, 2018
Construction and expansion of two thousand and eight [member]  
Disclosure Of Tax Exemption [line items]  
Tax-exemption Period, Start 2015
Tax-exemption Period, End 2019
Construction and expansion of two thousand and nine [member]  
Disclosure Of Tax Exemption [line items]  
Tax-exemption Period, Start 2018
Tax-exemption Period, End 2022