Warrants - Schedule of Key Terms of Placement Warrants (Detail) - $ / shares	9 Months Ended
	Sep. 30, 2018	Jan. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants Exercised	44,183
Warrants Outstanding	3,022,581
2017 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Issuance Date	2017-01
Term	7 years
Exercise Price Per Share	$ 3.17	$ 3.17
Warrants Outstanding	1,711,123
2016 Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Issuance Date	2016-08
Issuance Date	2016-09
Term	7 years
Exercise Price Per Share	$ 2.95
Warrants Exercised	44,183
Warrants Outstanding	1,311,458