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Leases - Additional Information (Detail) $ in Thousands |  | 9 Months Ended |
--- | --- | --- | ---
Nov. 11, 2019 USD ($) ft² | Sep. 30, 2021 USD ($) m² ft² | Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items] |  |  |
Operating lease, liability |  | $ 6,108 |
Right-of-use assets |  | $ 9,071 | $ 7,960
Waltham Lease |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Current office space under lease agreement | ft² |  | 6,000 |
Operating lease expiration (years) |  | 5 years |
Current base rent |  | $ 263 |
Lease, term of contract (years) |  | 5 years |
Vienna Lease |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Current office space under lease agreement | m² |  | 400 |
Current base rent |  | $ 154 |
Lease, term of contract (years) |  | 2 years |
Office space | m² |  | 1,200 |
Lease not yet commenced, term of contract |  | 7 years |
Building improvements |  | $ 709 |
Annual base rent |  | $ 300 |
Allston Lease |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Current office space under lease agreement | ft² | 28,000 |  |
Lease not yet commenced | $ 1,000 |  |
Lease, renewal term of contract (years) | 5 years |  |

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- Definition Term of lessee's operating lease not yet commenced, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980 + Details
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- Definition Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980 + Details
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977 + Details
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