COMMITMENTS AND CONTINGENCIES - Additional Information (Details)					1 Months Ended						3 Months Ended				6 Months Ended	9 Months Ended
	Feb. 10, 2021	Apr. 02, 2020	Mar. 11, 2020	Jan. 01, 2017 USD ($)	May 31, 2023 USD ($)	Feb. 28, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020	Feb. 28, 2019 USD ($)	Jul. 31, 2016 USD ($) ft²	Sep. 30, 2023 USD ($) ft² extensionOption	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) ft² extensionOption	Sep. 30, 2022 USD ($)	Dec. 22, 2022 USD ($) quarterPeriod	Nov. 30, 2020 ft²	Apr. 30, 2018 ft²
Commitments And Contingencies [Line Items]
Operating lease, cost											$ 1,200,000			$ 1,800,000		$ 4,400,000	$ 5,400,000
Operating lease, payments											1,400,000			1,800,000		4,500,000	5,500,000
Loss on termination of lease											$ 0	$ 500,000		0	$ 500,000	$ 524,000	0
Operating lease, remaining lease term											2 years 11 months 12 days					2 years 11 months 12 days
Contract cost incurred in research and development activities																$ 45,400,000
Supply Agreement, Patheon Inc.
Commitments And Contingencies [Line Items]
Purchase commitment, option for non-auto renewal, prior written notice period			18 months
Minimum purchase commitment											$ 0					$ 0
Siegfried Evionnaz SA
Commitments And Contingencies [Line Items]
Purchase commitment, option to extend, prior notice period																12 months
Cost of purchased minimum quantity product											18,100,000					$ 18,100,000
STA Pharmaceutical Hong Kong Limited
Commitments And Contingencies [Line Items]
Minimum purchase commitment, initial term		4 years
Long-term minimum purchase commitment																14,900,000
WuXi STA
Commitments And Contingencies [Line Items]
Purchase commitment, option to extend, prior notice period	18 months
Minimum purchase commitment, initial term	4 years
Long-term purchase commitment, fixed price, period	12 months
Long-term purchase commitment, option to terminate, prior notice period (at least)	180 days
BioVectra Inc
Commitments And Contingencies [Line Items]
Long-term purchase commitment, termination amount payable																		$ 32,500,000
Long-term purchase commitment, upfront payment termination amount													$ 17,500,000
Long-term purchase commitment, termination amount payable after upfront payment, number of quarterly periods | quarterPeriod																		6
Long-term purchase commitment, termination amount payable after upfront payment, per quarter																		$ 2,500,000
Long-term purchase commitment, termination amount payable after upfront payment																		$ 15,000,000
Long-term purchase commitment, imputed interest on termination amount payable																		17.00%
Long-term purchase commitment, upfront termination amount classified as cost of goods sold													$ 11,200,000
Amortization discount											$ 500,000					$ 1,400,000
Minimum
Commitments And Contingencies [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term											6.65%					6.65%
Maximum
Commitments And Contingencies [Line Items]
Operating lease, incremental borrowing rates based on remaining lease term											6.94%					6.94%
Cambridge
Commitments And Contingencies [Line Items]
Area of property leased (in square feet) | ft²										45,362									65,167
Annual lease expense										$ 200,000
Monthly lease expense				$ 22,000
Cambridge | Letter of Credit | Other Assets
Commitments And Contingencies [Line Items]
Total security deposit in connection with lease											$ 1,600,000					$ 1,600,000
Cambridge | Office Space
Commitments And Contingencies [Line Items]
Area of property leased (in square feet) | ft²																				19,805
Monthly lease expense							$ 48,000		$ 100,000
Operating lease, free monthly rent, period								2 months
Lease period, number of extension options | extensionOption											1					1
Lease extension period											5 years					5 years
Boston | Office Space
Commitments And Contingencies [Line Items]
Area of property leased (in square feet) | ft²											27,924					27,924
Monthly lease expense						$ 200,000
Operating lease, free monthly rent, period						5 months
Operating lease, annual rent escalation, percentage						2.00%
Payments to transfer rights and obligations of operating lease					$ 1,300,000
Proceeds from return of security deposit in connection with lease															$ 1,000,000
Boston | Office Space | Keryx Biopharmaceuticals, Inc.
Commitments And Contingencies [Line Items]
Sublease rental income														$ 500,000		$ 300,000	$ 1,400,000