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Fair Value of Financial Assets and Liabilities - Additional Information (Detail)
6 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Transfer of assets from level 1 to level 2 $ 0 $ 0
Transfer of assets from level 2 to level 1 0 0
Transfer of liabilities from level 1 to level 2 0 0
Transfer of liabilities from level 2 to level 1 $ 0 $ 0
Fair value determination model Monte-Carlo simulation analysis  
Expected Term of Instrument [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Expected term 1 year 6 months 2 years
Expected Stock Volatility [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Derivative liability, measurement input 80.0 80.0
Risk-free Interest Rate [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Derivative liability, measurement input 2.40 1.87