Leases (Details) $ in Thousands				1 Months Ended	6 Months Ended	12 Months Ended
	Sep. 01, 2020 USD ($) ft²	Nov. 11, 2019 USD ($) ft²	Mar. 13, 2019 USD ($) ft²	Aug. 31, 2017 USD ($) ft²	Jul. 31, 2021	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Right-of-use assets						$ 7,960	$ 1,959
Operating lease, liability						5,270
Lease liabilities						4,484	1,918
Current portion of lease liability						786	$ 898
Right-of-use asset, amortization term			5 years
Cambridge Lease
Lessee, Lease, Description [Line Items]
Office space area | ft²				13,000
Base rent				$ 832
Security deposit liability						264
Waltham Lease
Lessee, Lease, Description [Line Items]
Office space area | ft²			6,000
Base rent			$ 263
Term of contract			5 years
2019 Vienna Lease
Lessee, Lease, Description [Line Items]
Office space area | ft²			400
Base rent			$ 154
Term of contract			2 years
Boston Lease
Lessee, Lease, Description [Line Items]
Right-of-use assets	$ 8,000
Operating lease, liability	$ 4,600
Office space area | ft²		28,000
Renewal term		5 years
Lease not yet commenced, amount		$ 1,000
Security deposit liability		$ 1,100
New Vienna Lease [Member]
Lessee, Lease, Description [Line Items]
Office space area | ft²	1,200
Base rent	$ 300
Term of contract	7 years
Future Unreimbursed Expenditures Expected To Be Incurred						$ 675
New Vienna Lease [Member] | Forecast
Lessee, Lease, Description [Line Items]
Rent-free period					6 months
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Right-of-use assets								$ 2,000
Operating lease, liability								2,500
Lease liabilities								1,900
Current portion of lease liability								613
Net deferred rent								$ (512)