Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($)		9 Months Ended
	Nov. 18, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Organization And Significant Accounting Policies [Line Items]
Cash and cash equivalents		$ 38,383,135	$ 43,616,543	$ 85,366,448	$ 81,214,354
Short term investments		36,754,754
Net increase (decrease) in cash and investments		(10,200,000)
Cash outflows related to operating activities excluding upfront payment from Amgen		(44,700,000)
Capital expenditures		7,810,754	$ 1,147,748
Proceeds from the issuance of common stock		12,419,119
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
Amgen
Organization And Significant Accounting Policies [Line Items]
Proceeds from upfront payments and equity investments		$ 42,500,000
Amgen | Common Stock Purchase Agreement
Organization And Significant Accounting Policies [Line Items]
Proceeds from the issuance of common stock	$ 12,500,000
Amgen | ARO-LPA Agreement
Organization And Significant Accounting Policies [Line Items]
Common stock issued	1,745,810
Upfront payment	$ 30,000,000
Amgen | ARO-LPA Agreement | Common Stock Purchase Agreement
Organization And Significant Accounting Policies [Line Items]
Common stock issued	1,745,810