COMMITMENTS AND CONTINGENCIES (Details)	1 Months Ended					12 Months Ended
	Dec. 31, 2022 USD ($)	Jul. 31, 2022 USD ($) ft²	May 31, 2022 USD ($)	Apr. 30, 2022 USD ($) ft²	Dec. 31, 2021 USD ($) shares	Dec. 31, 2022 USD ($) renewal_term	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Mar. 31, 2021 USD ($)	Oct. 31, 2020 USD ($)
Commitments and Contingencies [Line Items]
Number of renewal terms (up to) | renewal_term						3
Lessee, operating lease, renewal term	3 years	3 years		3 years		3 years
Operating lease right-of-use asset	$ 1,610,000				$ 1,680,000	$ 1,610,000	$ 1,680,000		$ 1,600,000	$ 100,000
Lease discount rate									6.00%	6.00%
Lease remaining term									12 months
Operating lease liability, short-term	$ 613,000				$ 520,000	$ 613,000	$ 520,000			$ 100,000
Area of office space expanded | ft²		5,240		2,432
Area of office space terminated | ft²		1,087		1,087
Area of office space extension | ft²		3,284		3,284
Operating lease, annual base rent		$ 900,000		$ 400,000
Lessee, operating lease, term of contract		4 years
Operating lease, liability, current, statement of financial position [Extensible List]	Accrued liabilities				Accrued liabilities	Accrued liabilities	Accrued liabilities			Accrued liabilities
Operating lease liability noncurrent	$ 1,100,000					$ 1,100,000
Operating lease, liability, noncurrent, statement of financial position [Extensible List]	Other liabilities					Other liabilities
Amortization (reversal of amortization) expense relating to operating lease right-of-use assets						$ 500,000	$ 500,000
Operating expenses of leases						$ 300,000	300,000
ImmunoGen, Inc
Commitments and Contingencies [Line Items]
Milestone payments										$ 48,000,000
Collaborative arrangement, milestone payment	$ 10,000,000		$ 3,000,000		$ 2,500,000
Potential royalty payments										$ 95,000,000
Xencor, Inc
Commitments and Contingencies [Line Items]
Milestone payments					27,750,000		27,750,000	$ 30,000,000
Potential royalty payments					$ 20,000,000		$ 20,000,000	$ 25,000,000
Collaboration arrangement, research license and selection rights, term					1 year
Shares issued in exchange for rights granted (in shares) | shares					394,737		394,737	322,407
Value of shares issued in exchange for rights granted							$ 7,500,000	$ 6,000,000
Collaboration arrangement, potential development milestone payment, maximum					$ 4,750,000		4,750,000
Collaborative arrangement, potential special payments, maximum					$ 3,000,000		$ 3,000,000