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Other Financial Assets and Financial Liabilities - Description of Significant Unobservable Inputs to Valuation (Parenthetical) (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Available-for-sale financial assets [Member]    
Disclosure of significant unobservable inputs used in fair value measurement of assets [Line Items]    
Increase in fair value due to a decrease in the liquidity discount $ 203 $ 204