Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Reconciliation of Company's Financial Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail)

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Fair Value Measurements - Reconciliation of Company's Financial Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Level 3) (Detail) - Warrant Liabilities [Member] - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Balance at beginning of period $ 12,778,781 $ 256,054 $ 12,698,980 $ 444,324
Increase (decrease) in fair value (3,196,865) (70,395) (3,117,064) (258,665)
Balance at end of period $ 9,581,916 $ 185,659 $ 9,581,916 $ 185,659