Fair Value Measurement - Additional Information (Detail) - USD ($)					9 Months Ended
	Sep. 20, 2018	Aug. 13, 2018	Jan. 30, 2018	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fixed asset purchases as equipment financings obligations					$ 270,000	$ 363,000
Issuance of unregistered warrants to purchase shares of common stock, grant date fair value	$ 2,000,000	$ 8,400,000	$ 9,700,000	$ 2,800,000
Issuance of unregistered warrants to purchase shares of common stock	762,438	2,549,140	1,095,153	72,000
Estimated grant date fair value of warrants	$ 2.57	$ 3.30	$ 8.82
Exercise price of warrants		$ 4.53	$ 4.53	$ 75.00
Class of warrant or rights, term		5 years	5 years
Prefunded Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Exercise price of warrants	$ 3.275
Issuance of warrants to purchase shares of common stock	120,000
Common stock warrants outstanding, intrinsic value	$ 350,000
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 warrants	$ 3.16	$ 4.53	$ 4.53
Class of warrant or rights, term	5 years	5 years	5 years
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 equipment financings obligations					$ 274,000