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 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]        
Balance at beginning of period $ 4,345,902 $ 38,626,579 $ 20,781,663 $ 13,549,437
(Decrease) increase in fair value [1] (2,186,710) (3,246,765) (18,622,471) 21,830,377
Balance at end of period $ 2,159,192 $ 35,379,814 $ 2,159,192 $ 35,379,814
[1] The change in fair values of the warrant liabilities is recorded in other income (expense) in the consolidated statement of operations.