Commitments and Contingencies (Details) - USD ($) $ in Millions		12 Months Ended
	Dec. 07, 2018	Mar. 31, 2020
Third Parties for Pharmaceutical Manufacturing and Research Activities
Other Commitments [Line Items]
Termination notice term, uncured material breach		30 days
Oxford BioMedica (UK) Ltd.
Other Commitments [Line Items]
License agreement, termination notice prior term		2 months
The University of Massachusetts Medical School
Other Commitments [Line Items]
Termination notice term, uncured material breach	90 days	90 days
Termination notice term	60 days	60 days
cGMP Grade Viral Vector Production
Other Commitments [Line Items]
Purchase commitment, remaining minimum amount		$ 1.4