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Collaboration and License Agreements - Janssen Pharmaceuticals, Inc - Additional Information (Detail)		1 Months Ended	3 Months Ended		6 Months Ended
	Oct. 03, 2018 USD ($) Obligation	Oct. 31, 2018 USD ($) Target $ / shares shares	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Apr. 30, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock					$ 60,521,729	$ 56,585,035
Revenues			$ 48,148,275	$ 650,125	82,806,171	$ 4,159,946
Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 226,300,000
JJDC \| Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued \| shares		3,260,869
Stock issued, price per share \| $ / shares		$ 23.00
Janssen and JJDC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues			47,900,000		82,500,000
Contract assets			13,300,000		13,300,000
Contract liabilities			$ 120,600,000		120,600,000
Janssen and JJDC \| Common Stock Purchase Agreement
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
Janssen and JJDC \| Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock		75,000,000			75,000,000
Cash received as due under collaboration agreement		175,000,000			$ 175,000,000
Janssen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct performance obligations \| Obligation	1
Janssen \| Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Janssen \| License Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments		$ 1,600,000,000
Janssen \| Research Collaboration and Option Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
Number of additional targets for development, regulatory and sales milestone payments \| Target		3
Janssen \| Collaboration Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development, regulatory and sales milestones payments		$ 1,900,000,000
Janssen \| JNJ-3989 (ARO-HBV) Agreement \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment							$ 25,000,000