Stockholders' Equity - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Jan. 22, 2018	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Class Of Stock [Line Items]
Capital stock authorized for issuance			150,000,000
Common stock, shares authorized			145,000,000	145,000,000
Common stock, par value			$ 0.001	$ 0.001
Preferred stock, shares authorized			5,000,000
Preferred stock, par value			$ 0.001
Common stock, shares outstanding			88,505,302	74,785,726
Public offering price per share			$ 5.25
Proceeds from the issuance of common stock			$ 56,585,035	$ 12,419,119	$ 52,231,433
Underwritten Public Offering
Class Of Stock [Line Items]
Common stock shares sold	11,500,000
Public offering price per share	$ 5.25
Net proceeds, after deducting underwriting commissions and discounts and offering expenses payable	$ 56,600,000
Common Stock Purchase Agreement | JJDC | Subsequent Event
Class Of Stock [Line Items]
Public offering price per share		$ 23.00
Shares issued		3,260,869
Proceeds from the issuance of common stock		$ 75,000,000
2004 Equity Incentive Plan, 2013 Equity Incentive Plan, and Inducement Grants
Class Of Stock [Line Items]
Common Stock, Share reserve for issuance			8,732,569