Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		9 Months Ended
	Oct. 10, 2018	Oct. 01, 2018	Nov. 06, 2018	Jan. 31, 2018	Sep. 30, 2018
Subsequent Event [Line Items]
Net proceeds of offering after deducting underwriting discounts and commissions					$ 8,164
Stock options granted					1,530,150
Stock options exercise price, lower range					$ 0.75628
Stock options exercise price, upper range					$ 9.97
Stock options cancelled					32,001
Common Stock [Member]
Subsequent Event [Line Items]
Shares issued				2,691,494
Combined purchase price				$ 2.35
Net proceeds of offering after deducting underwriting discounts and commissions				$ 5,700
At-The-Market Sales Agreement [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Shares issued					5,766,247
Net proceeds of offering after deducting underwriting discounts and commissions					$ 4,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock options vesting period		4 years
Threshold days for performance criteria		60 days
Subsequent Event [Member] | Minimum [Member]
Subsequent Event [Line Items]
Share price		$ 19.92
Subsequent Event [Member] | Stock Option Repricing [Member]
Subsequent Event [Line Items]
Stock options granted		2,774,140
Stock options reduced exercise price		$ 0.568
Subsequent Event [Member] | Performance Options [Member] | Gridley [Member]
Subsequent Event [Line Items]
Stock options cancelled		60,000
Subsequent Event [Member] | Performance Options [Member] | Lieber [Member]
Subsequent Event [Line Items]
Stock options cancelled		30,000
Subsequent Event [Member] | Performance Options [Member] | Kennedy [Member]
Subsequent Event [Line Items]
Stock options cancelled		30,000
Subsequent Event [Member] | Underwritten Public Offering [Member]
Subsequent Event [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
Warrant exercise price	$ 0.70
Warrants exercisable term	5 years
Subsequent Event [Member] | Underwritten Public Offering [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Shares issued	26,155,000
Subsequent Event [Member] | Underwritten Public Offering [Member] | Common Stock and Warrants [Member]
Subsequent Event [Line Items]
Combined purchase price	$ 0.65
Subsequent Event [Member] | At-The-Market Sales Agreement [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Shares issued			867,656
Net proceeds of offering after deducting underwriting discounts and commissions			$ 500