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 ($)
Jun. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities $ 16,829,854 $ 31,354,170
Warrant liabilities (9,581,916) (12,698,980)
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 4,635,099 3,411,058
Marketable securities 16,829,854 31,354,170
Total assets (liabilities) 21,464,953 34,765,228
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Warrant liabilities (9,581,916) (12,698,980)
Total assets (liabilities) $ (9,581,916) $ (12,698,980)