Collaboration and License Agreements - Janssen Pharmaceuticals, Inc - Additional Information (Detail)		1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 03, 2018 USD ($) Target Obligation	Dec. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Proceeds from the issuance of common stock		$ 250,500,000			$ 250,478,974	$ 60,521,729
Revenues			$ 27,375,778	$ 42,696,636	80,359,211	125,502,807
Deferred revenue			26,274,362		26,274,362		$ 77,769,629
Collaboration and License agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Initial transaction price	$ 252,600,000
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
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment	$ 25,000,000		25,000,000		25,000,000
Number of distinct performance obligations | Obligation	1
Revenues			6,900,000	42,300,000	57,900,000	124,800,000
Contract assets			0		0
Deferred revenue			26,300,000		26,300,000
Janssen | ARO-JNJ1
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues			400,000	$ 400,000	2,400,000	$ 400,000
Contract assets			1,700,000		1,700,000
Deferred revenue			$ 0		$ 0
JJDC | Common Stock Purchase Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Oct. 03, 2018
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]
Cash received as due under collaboration agreement	$ 175,000,000