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Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($)		6 Months Ended
	Jan. 22, 2018	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Organization And Significant Accounting Policies [Line Items]
Public offering price per share		$ 5.25
Cash and cash equivalents		$ 69,805,117	$ 61,718,971	$ 24,838,567	$ 85,366,448
Short term investments		21,736,820		40,769,539
Net increase (decrease) in cash and investments		25,900,000
Net proceeds received from public offering		56,585,035	12,691,937
Cash outflows related to operating activities		(30,133,934)	$ (4,325,866)
Restricted Cash		0		0
Fair value of contingent consideration obligation due to discontinuation of clinical trials		0		$ 0
Maximum
Organization And Significant Accounting Policies [Line Items]
Amount insured in FDIC per account		$ 250,000
Property, Plant and Equipment, Useful Life		7 years
Minimum
Organization And Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life		3 years
Underwritten Public Offering
Organization And Significant Accounting Policies [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

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