LEASES - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2023 USD ($)	Jun. 30, 2024 USD ($) ft² extension_option	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) ft² extension_option	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, remaining lease term		2 years 2 months 12 days		2 years 2 months 12 days
Operating lease, cost		$ 1,200	$ 1,400	$ 2,500	$ 3,200
Operating lease, payments		1,400	1,400	2,900	3,100
Loss on termination of lease		$ 0	524	$ 0	524
Minimum
Lessee, Lease, Description [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term		6.65%		6.65%
Maximum
Lessee, Lease, Description [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term		6.94%		6.94%
Cambridge
Lessee, Lease, Description [Line Items]
Area of property leased (in square feet) | ft²		65,167		65,167
Cambridge | Other Assets | Letter of Credit
Lessee, Lease, Description [Line Items]
Total security deposit in connection with lease		$ 1,700		$ 1,700		$ 1,700
Cambridge | Office And Storage Space
Lessee, Lease, Description [Line Items]
Leased area subject to expiration | ft²		59,216		59,216
Operating lease extensions (in extension options) | extension_option		1		1
Lease extension period		5 years		5 years
Cambridge | Laboratory Space
Lessee, Lease, Description [Line Items]
Leased area subject to expiration | ft²		5,951		5,951
Operating lease extensions (in extension options) | extension_option		1		1
Lease extension period		2 years		2 years
Boston | Office Space
Lessee, Lease, Description [Line Items]
Area of property leased (in square feet) | ft²		27,924		27,924
Payments to transfer rights and obligations of operating lease	$ 1,300
Boston | Office Space | Keryx Biopharmaceuticals, Inc.
Lessee, Lease, Description [Line Items]
Sublease rental income		$ 0	$ 0	$ 0	$ 300