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
Mar. 31, 2019
Mar. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Balance at beginning of period $ 20,781,663 $ 13,549,437
(Decrease) increase in fair value [1] (17,799,629) 12,274,559
Balance at end of period $ 2,982,034 $ 25,823,996
[1] The change in fair values of the warrant liabilities is recorded in other income (expense) in the consolidated statement of operations.