Leases - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended							12 Months Ended
	Oct. 31, 2022	Feb. 28, 2022	Sep. 30, 2021	Feb. 28, 2021	Sep. 30, 2019	Jul. 31, 2019	Mar. 31, 2019	Dec. 31, 2022	Dec. 31, 2021
Leases [Line Items]
Expiration date								Dec. 31, 2023
ROU asset								$ 31,633	$ 29,743
Lease liability								35,387
Operating lease costs								6,600	6,200
Cash paid for operating lease								4,800	5,200
Variable lease costs								$ 3,700	$ 14,500
Operating lease, weighted average remaining lease term								6 years 11 months 4 days
Operating lease, weighted average discount rate, percent								6.23%
DMS Agreement
Leases [Line Items]
Lease expiration month and year						2021-07
Lease, option to extend								Effective June 2022, the Company entered into a First Amendment to the DMS Agreement to extend the expiration date to June 2024 provided that the terms and conditions of the DMS Agreement will continue to apply to any active SOW's. The DMS Agreement (or any individual SOW) may be terminated earlier by AlloVir at any time by providing 190 days’ notice.
Operating lease, existence of option to terminate						true
Lease, option to terminate								The DMS Agreement (or any individual SOW) may be terminated earlier by AlloVir at any time by providing 190 days’ notice.
Lease renewal term					2 years
Estimated lease term					3 years 9 months		4 years 3 months
Estimated lease expiring month and year					2023-07		2023-07
ROU asset					$ 6,300		$ 6,900
Lease liability					$ 6,300		$ 6,900
2020 DMS Agreement
Leases [Line Items]
Term of agreement				1 year
Lease renewal term				1 year
Estimated lease term				2 years
Estimated lease expiring month and year				2023-01
ROU asset				$ 3,100
Lease liability				2,500
Utilization fee				$ 3,200
Lessee operating lease, lease term including renewal option				2 years
Prepaid utilization fee				$ 600
Waltham Leases
Leases [Line Items]
Expiration date			Jul. 30, 2030
Operating lease, existence of option to extend			true
Lease, option to extend								The Company has the option to renew the leased space for an additional one time period of five years with written notice from the Company. As of December 31, 2022, the Company has no reasonable certainty that this option to extend will be exercised.
Lease commencement month and year			2021-09
Additional one time lease period			5 years
Tenant improvement allowance to be reimbursed			$ 3,100
Tenant improvement allowance, reimbursement period			2 years
Tenant improvement allowance								$ 900
New Lease Agreement with BP Bay Colony LLC
Leases [Line Items]
ROU asset			$ 6,000
Lease liability			6,000
Sublease with AMAG Pharmaceuticals
Leases [Line Items]
ROU asset			17,300
Lease liability			$ 17,300
Original SOW Amendment under DMS Agreement | Lease Modification under ASC 842
Leases [Line Items]
ROU asset		$ (1,400)
Lease liability		$ (1,400)
Second SOW Amendment under DMS Agreement
Leases [Line Items]
Lease expiration month and year		2022-02
Second SOW Amendment under DMS Agreement | Lease Modification under ASC 842
Leases [Line Items]
ROU asset		$ (2,600)
Lease liability		(2,600)
2022 SOW Under the DMS Agreement
Leases [Line Items]
Lease expiration month and year	2024-12
ROU asset	$ 14,700
Lease liability	14,700
Utilization fee	$ 16,300
Lessee operating lease, lease term including renewal option	2 years 3 months
Change Order to Modify Terms of SOW under 2020 DMS Agreement | Lease Modification under ASC 842
Leases [Line Items]
ROU asset		(1,500)
Lease liability		$ (1,300)