Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Information about Company's Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)

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Fair Value Measurements - Information about Company's Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
Sep. 30, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities $ 26,645,137 $ 39,858,864
Warrant liabilities (35,379,814) (13,549,437)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 10,237,703 5,949,477
Marketable securities 26,645,137 39,858,864
Total assets (liabilities) 36,882,840 45,808,341
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Warrant liabilities 35,379,814 13,549,437
Total assets (liabilities) $ 35,379,814 $ 13,549,437