Warrants - Schedule of Key Terms of Placement Warrants (Detail) - $ / shares	1 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants Exercised		385,627
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 Exercised		1,591	9,389
Warrants Outstanding		1,709,532	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	7 years
Exercise Price Per Share	$ 2.95	$ 2.95
Warrants Exercised		225,026	25,104
Warrants Outstanding		1,130,615	1,355,641
2016 and 2017 Private Placement Warrants
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants Exercised		226,617	34,493	0
Warrants Outstanding		2,840,147	3,066,764