Nature of Business - Additional Information (Detail) - USD ($)			1 Months Ended		9 Months Ended
	Oct. 10, 2018	Sep. 29, 2016	Nov. 06, 2018	Jan. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds of offering after deducting underwriting discounts and commissions					$ 8,164,000
Accumulated deficit					$ 216,012,000	$ 208,187,000
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued				2,691,494
Net proceeds of offering after deducting underwriting discounts and commissions				$ 5,700,000
Combined purchase price				$ 2.35
Private Placement [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Proceeds from issuance of common stock, preferred stock and warrants, net of issuance costs		$ 27,600,000
Class of Warrants or right to purchase common stock		13,333,334
Combined purchase price		$ 2.25
Warrant exercise price		$ 2.25			$ 2.25
Private Placement [Member] | Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued		2,596,059
At-The-Market Sales Agreement [Member] | Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued					5,766,247
Net proceeds of offering after deducting underwriting discounts and commissions					$ 4,000,000
At-The-Market Sales Agreement [Member] | Common Stock [Member] | Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued			867,656
Net proceeds of offering after deducting underwriting discounts and commissions			$ 500,000
At-The-Market Sales Agreement [Member] | Common Stock [Member] | Maximum [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Aggregate offering price of shares					$ 10,000,000
Underwritten Public Offering [Member] | Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Class of Warrants or right to purchase common stock	19,616,250
Gross proceeds from offering, before deducting underwriting discounts and commissions and offering expenses	$ 17,000,000
Warrant exercise price	$ 0.70
Warrants exercisable term	5 years
Underwritten Public Offering [Member] | Common Stock [Member] | Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued	26,155,000
Underwritten Public Offering [Member] | Common Stock and Warrants [Member] | Subsequent Event [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Combined purchase price	$ 0.65