Common Stock - Additional Information (Detail) - USD ($)			1 Months Ended						6 Months Ended
	Jul. 16, 2018	Jan. 29, 2018	Jan. 31, 2018	Dec. 31, 2017	Jul. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	May 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Feb. 28, 2018	Nov. 30, 2017	Feb. 28, 2015
Class of Stock [Line Items]
Common stock sales agreement, aggregate offering amount				$ 118,000					$ 119,000
Common stock, shares issued				118,325,000					118,995,000
Underwriters' option to purchase shares									145,617
Gross proceeds from public offering									$ 518,000	$ 21,035,000
Cash proceeds										$ 3,210,000
Underwritten Public Offering
Class of Stock [Line Items]
Common stock, shares issued							34,500,000
Underwriters' option to purchase shares							4,500,000
Gross proceeds from public offering							$ 17,300,000
Percentage of affiliates stock holders							5.00%
Net proceeds from public offering							$ 15,400,000
Private Placement | PIPE Warrants
Class of Stock [Line Items]
Warrants exercisable period								5 years
Warrants exercise price								$ 1.00	$ 1.00
Common stock, shares issued			518,134		259,067			17,642,482
Shares issued, price per share								$ 0.965
Gross proceeds from issuance of private placement								$ 17,000,000
Exchange of unit to share								1	1
Warrants exercisable shares of common stock exercised			518,134		259,067				777,201
Cash proceeds in connection with warrants exercised								$ 800,000
Warrants exercisable shares of common stock outstanding									16,865,281
Cash proceeds			$ 500,000		$ 300,000
Private Placement | PIPE Warrants | Director and Executive Officer
Class of Stock [Line Items]
Common stock, shares issued					259,067			544,039
Net offering proceeds to the company								$ 15,400,000
Cash proceeds					$ 300,000
Leerink
Class of Stock [Line Items]
Common stock, shares issued											0
New Enterprise Associates | Underwritten Public Offering
Class of Stock [Line Items]
Common stock, shares issued							420,000
Other Investors | Underwritten Public Offering
Class of Stock [Line Items]
Common stock, shares issued							6,000,000
F B R Co
Class of Stock [Line Items]
Common stock, shares issued						6,500,000				6,500,000
proceeds from sale of shares						$ 8,800,000
Minimum | Underwritten Public Offering
Class of Stock [Line Items]
Shares issued, price per share							$ 0.50
Maximum
Class of Stock [Line Items]
Offering, issuance and sale of stocks and securities, shelf registration												$ 200,000,000
Maximum | Leerink
Class of Stock [Line Items]
Common stock sales agreement, aggregate offering amount											$ 50,000,000
Common stock sales agreement commission, percentage											3.00%
Maximum | F B R Co
Class of Stock [Line Items]
Common stock sales agreement, aggregate offering amount													$ 17,900,000
Common stock sales agreement commission, percentage													3.00%
Settlement Warrants
Class of Stock [Line Items]
Warrants to purchase of common stock shares				2,000,000
Warrants exercisable period		1 year		1 year
Warrants exercise price				$ 3.00
Subsequent Event | Settlement Warrants
Class of Stock [Line Items]
Warrants to purchase of common stock shares	2,000,000
Warrants exercisable period	1 year
Warrants exercise price	$ 3.00