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Collaboration and License Agreements - Janssen Pharmaceuticals, Inc - Additional Information (Detail)		1 Months Ended		12 Months Ended
	Oct. 03, 2018 USD ($) Obligation	Nov. 30, 2018 USD ($)	Oct. 31, 2018 USD ($) Target $ / shares shares	Sep. 30, 2018 USD ($) $ / shares	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Stock issued, price per share \| $ / shares				$ 5.25
Proceeds from the issuance of common stock				$ 56,585,035	$ 12,419,119	$ 52,231,433
Collaboration and License agreements \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash received as due under collaboration agreement	$ 197,800,000
Initial transaction price	$ 197,800,000
Janssen \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct performance obligations \| Obligation	1
Janssen \| Common Stock Purchase Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement \| Maximum \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments			$ 1,600,000,000
Janssen \| Research Collaboration and Option Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| Collaboration Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of additional targets for development, regulatory and sales milestone payments \| Target			3
Janssen \| Collaboration Agreement \| Maximum \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments			$ 1,900,000,000
Janssen Pharmaceuticals Inc \| Common Stock Purchase Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen Pharmaceuticals Inc \| Research Collaboration and Option Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
JJDC \| Common Stock Purchase Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued \| shares			3,260,869
Stock issued, price per share \| $ / shares			$ 23.00
Proceeds from the issuance of common stock			$ 75,000,000
JJDC \| Collaboration and License agreements \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Cash received as due under collaboration agreement		$ 175,000,000	175,000,000
Proceeds from the issuance of common stock			$ 75,000,000