Related Party Transactions - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	May 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Research and Development
Related Party Transaction [Line Items]
Expenses incurred for annual maintenance fee		$ 0.3
REGENXBIO Option Genes License
Related Party Transaction [Line Items]
Expenses incurred for annual maintenance fee	$ 0.1
REGENXBIO Option Genes License | Research and Development
Related Party Transaction [Line Items]
Additional upfront fee paid			$ 0.6
Aggregate payments to related parties			$ 1.8