License and Collaboration Agreements License and Collaboration Agreements (Details) - USD ($)		3 Months Ended
	Jun. 05, 2018	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Oct. 31, 2019
License Agreement [Line Items]
Capitalized costs, current		$ 6,789,000		$ 6,951,000
Oxford BioMedica (UK) Ltd.
License Agreement [Line Items]
Payments for license agreement		500,000	$ 1,300,000
Payments for license and collaboration agreement, development and regulatory milestones, achieved during period			13,000,000.0
License agreement costs		1,700,000	1,400,000
Benitec Biopharma Limited
License Agreement [Line Items]
Payments for license agreement			700,000
License agreement costs			1,800,000
The University of Massachusetts Medical School
License Agreement [Line Items]
Payments for license agreement		0	1,000,000.0
License agreement costs		400,000	$ 1,000,000.0
Additional payment due to UMMS					$ 1,000,000.0
Prepaid Expenses and Other Current Assets and Other Noncurrent Assets | Oxford BioMedica (UK) Ltd.
License Agreement [Line Items]
Payments for license agreement	$ 5,000,000.0
Prepaid Expenses and Other Current Assets | Oxford BioMedica (UK) Ltd.
License Agreement [Line Items]
Capitalized costs, current		$ 1,600,000