Leases - Narrative (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2025 USD ($)	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Nov. 30, 2025 USD ($)	Sep. 30, 2024 ft²	Aug. 31, 2024 ft²	Nov. 30, 2021
Lessee, Lease, Description [Line Items]
Restricted cash		$ 13,691	$ 14,062
Operating lease right-of-use assets		126,177	47,156
Total operating lease liability		116,427
Prepaid expenses		(2,939)	(6,777)
Total payments under dispute			10,800
Reduction in operating lease liabilities		5,362	6,461
60 First Street, Cambridge, Massachusetts Lease
Lessee, Lease, Description [Line Items]
Term of contract, lease not yet commenced (in years)							10 years
Operating lease, extension (in years)							10 years
Restricted cash		13,100	13,100
Operating lease right-of-use assets	$ 76,800	44,900
Total operating lease liability	78,600	33,600
Total payments under dispute				$ 10,900
60 First Street, Cambridge, Massachusetts Lease | Revision of Prior Period, Reclassification, Adjustment
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		11,300
Prepaid expenses		$ 11,300
480 Arsenal Amendment
Lessee, Lease, Description [Line Items]
Area of operating lease | ft²						16,000
480 Arsenal Amendment Expansion Space
Lessee, Lease, Description [Line Items]
Area of operating lease | ft²						9,400
500 Arsenal Lease
Lessee, Lease, Description [Line Items]
Term of contract, lease not yet commenced (in years)		11 months
Restricted cash		$ 600	$ 600
Operating lease right-of-use assets	7,000
Total operating lease liability	5,500
Area of operating lease | ft²					48,500
Tenant improvements		2,400
Reduction in operating lease liabilities	3,100
Reduction to operating lease right-of-use assets	$ 3,100
500 Arsenal Lease, Additional Tenant Improvement Allowance
Lessee, Lease, Description [Line Items]
Tenant improvements		$ 1,200