Fair Value Measurements - Summary of Reconciliation of Warrant Liability Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) - Fair Value Measurement, Recurring [Member] - Warrant Liability [Member] - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 3,701,277	$ 4,095,019
Change in fair value upon re-measurement	(433,392)	3,072,747
Reclassification to Additional Paid-in Capital due to warrant exercise		(1,399,091)
Reclassification to Additional Paid-in Capital due to warrant amendment	$ (3,267,885)
Ending balance		$ 5,768,675