LEASES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Sep. 30, 2023	May 01, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		$ 1,806	$ 1,300	$ 137
Noncurrent operating lease liabilities		1,679	$ 1,300	0
Lessee, operating lease, discount rate			7.41%
Gain on early termination of sublease	$ 600
Current operating lease liabilities		970		$ 401
Spectrum Pharmaceuticals, Inc.
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		400
Noncurrent operating lease liabilities		300
Current operating lease liabilities		$ 700