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Fair Value Information - Additional Information (Detail) - USD ($)
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]      
Fair value assets transfers from Level 1 to Level 2 $ 0   $ 0
Fair value assets transfers from Level 2 to Level 1 0   0
Fair value liabilities transfers from Level 1 to Level 2 0   0
Fair value liabilities transfers from Level 2 to Level 1 0   $ 0
Fair Value on Non-Recurring Basis [Member]      
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]      
Total assets $ 0 $ 74,000