Fair Value Measurement - Additional Information (Detail) - USD ($)				3 Months Ended
	Mar. 19, 2019	Feb. 12, 2019	Jan. 30, 2018	Mar. 31, 2019	Mar. 31, 2018	Aug. 13, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed asset purchases as right-of-use asset finance lease obligations				$ 149,000	$ 79,000
Estimated grant date fair value of warrants	$ 1.01	$ 0.95	$ 8.82
Issuance of unregistered warrants to purchase shares of common stock, grant date fair value	$ 6,000,000	$ 6,800,000	$ 9,700,000
Exercise price of unregistered warrants	$ 1.25	$ 1.20	$ 1.20			$ 4.53
Class of warrant or rights, term	5 years 6 months		5 years
Follow-on Public Offering [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Issuance of unregistered warrants to purchase shares of common stock, grant date fair value			$ 9,700,000
Exercise price of unregistered warrants	$ 1.25	$ 1.20	$ 1.20
Class of warrant or rights, term	5 years 6 months	5 years	5 years
Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Issuance of unregistered warrants to purchase shares of common stock	5,950,000	7,165,000	1,095,153
Estimated Fair Value Measurements, Nonrecurring [Member] | Level 3 Inputs [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed asset purchases as right-of-use asset finance lease obligations				$ 149,000