Collaboration and License Agreements - Horizon Therapeutics Ireland DAC - Additional Information (Detail) $ in Thousands		3 Months Ended		6 Months Ended
	Jun. 18, 2021 USD ($) Obligation Bundle	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jul. 31, 2021 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		$ 151,805	$ 32,811	$ 179,244	$ 54,113
Contract liabilities		97,869		97,869		$ 111,055
Horizon Therapeutics Ireland DAC | ARO-XDH
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Agreement date	Jun. 18, 2021
Cash received as due under collaboration agreement							$ 40,000
Number of distinct performance obligations | Obligation	1
Initial transaction price	$ 40,000
Revenues		6,700	0	13,300	0
Contract assets		0		0
Contract liabilities		20,000		20,000
Horizon Therapeutics Ireland DAC | License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of distinct bundle | Bundle	1
Number of distinct performance obligations | Obligation	1
Horizon Therapeutics Ireland DAC | ARO-XDH Supply Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		1,300	$ 0	1,300	$ 0
Contract assets		1,300		1,300
Contract liabilities		$ 0		$ 0
Horizon Therapeutics Ireland DAC | Maximum | ARO-XDH
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development regulatory and sales milestones payments	$ 660,000