SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) unit	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2021	Mar. 31, 2021	Jan. 01, 2019 USD ($)
Property, Plant and Equipment [Line Items]
Insurance coverage limit		$ 250,000	$ 250,000		$ 250,000
Intangibles impairment charge				$ 31,700,000	$ 31,700,000	$ 0	$ 0
Impairment of intangible assets						0
Number of reporting units | unit					1
Goodwill		$ 13,064,000	$ 13,064,000	$ 13,100,000	$ 13,064,000	13,064,000
Goodwill impairment					$ 0	$ 0
License agreement, royalty rate		2.00%	2.00%		2.00%
Index rate, high-yield		0.080	0.080	0.075	0.080	0.084		0.066	0.074
Lease liability		$ 124,000	$ 124,000		$ 124,000
Dividend yield					0.00%
License and related revenue					$ 26,544,000	$ 11,236,000	$ 0
Discount Rate
Property, Plant and Equipment [Line Items]
Weighted-average cost of capital		9.30%	9.30%	8.60%	9.30%	8.80%		6.80%	7.80%
Minimum
Property, Plant and Equipment [Line Items]
Probability of achieving clinical and regulatory milestones		45.00%	45.00%		45.00%
Maximum
Property, Plant and Equipment [Line Items]
Probability of achieving clinical and regulatory milestones		55.00%	55.00%		55.00%
Cumulative Effect, Period of Adoption, Adjustment
Property, Plant and Equipment [Line Items]
Right-of-use asset										$ 200,000
Lease liability										$ 200,000
Roche | Subsequent Event
Property, Plant and Equipment [Line Items]
Proceeds from milestone achieved	$ 20,000,000
Performance-Based Awards
Property, Plant and Equipment [Line Items]
Award vesting period					4 years
Expected term					10 years
Licensing Agreements | Roche
Property, Plant and Equipment [Line Items]
Milestone payment		$ 20,000,000
Milestone payment term		30 days
Vicinium | United States | IPR&D intangible assets:
Property, Plant and Equipment [Line Items]
Intangibles impairment charge					$ 31,700,000
EBI-031 | Roche
Property, Plant and Equipment [Line Items]
License and related revenue			$ 20,000,000
EBI-031 | Roche | Subsequent Event
Property, Plant and Equipment [Line Items]
Proceeds from milestone achieved	$ 20,000,000
EBI-031 | Roche | Minimum
Property, Plant and Equipment [Line Items]
License agreement, royalty rate		7.50%	7.50%		7.50%
EBI-031 | Roche | Maximum
Property, Plant and Equipment [Line Items]
License agreement, royalty rate		15.00%	15.00%		15.00%
Lab equipment
Property, Plant and Equipment [Line Items]
Estimated useful life					5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life					4 years
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated useful life					3 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated useful life					5 years