Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($)		1 Months Ended	12 Months Ended
	Nov. 18, 2016	Aug. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Nov. 29, 2016	Sep. 30, 2013
Schedule Of Investments [Line Items]
Cash and cash equivalents			$ 85,366,448	$ 81,214,354	$ 132,510,610		$ 19,114,444
Net increase (decrease) in cash			4,152,094	(51,296,256)	113,396,166
Proceeds from the issuance of common stock		$ 43,200,000	52,231,433		172,641,671
Proceeds from sale of marketable securities			17,308,000	26,090,950	11,591,120
Cash outflow related to continuing operating activities			(64,427,486)	(65,707,615)	$ (35,416,373)
Restricted Cash			0	$ 0
Maximum
Schedule Of Investments [Line Items]
Amount insured in FDIC per account			$ 250,000
Property, Plant and Equipment, Useful Life			7 years
Minimum
Schedule Of Investments [Line Items]
Property, Plant and Equipment, Useful Life			3 years
Common Stock Purchase Agreement | Amgen
Schedule Of Investments [Line Items]
Proceeds from the issuance of common stock			$ 9,000,000
Subsequent Event
Schedule Of Investments [Line Items]
Percentage of workforce reduced due to discontinued clinical program						30.00%
Subsequent Event | Amgen | Second Collaboration and License Agreement
Schedule Of Investments [Line Items]
Upfront payment	$ 30,000,000
Subsequent Event | Common Stock Purchase Agreement | Amgen
Schedule Of Investments [Line Items]
Proceeds from the issuance of common stock	$ 12,500,000
Subsequent Event | Common Stock Purchase Agreement | Amgen | Second Tranche
Schedule Of Investments [Line Items]
Common stock issued	1,745,810