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Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($)		3 Months Ended
	Jan. 22, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016
Organization And Significant Accounting Policies [Line Items]
Cash and cash equivalents		$ 11,531,345	$ 102,105,569	$ 24,838,567	$ 85,366,448
Short term investments		39,169,376		40,769,539
Net increase (decrease) in cash and investments		(14,900,000)
Cash outflows related to operating activities		(14,690,480)	$ 10,000,191
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
Subsequent Events | 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	$ 56,700,000

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Amount of liability recognized arising from contingent consideration in a business combination, expected to be settled beyond one year or the normal operating cycle, if longer.

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