LICENSE AGREEMENTS AND COMMITMENTS - CD33 License Agreement (Details) - CD33 License Agreement - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Nov. 13, 2017
Agreements
Annual minimum royalties payable						$ 40
Annual minimum royalties payable from tenth anniversary						60
Clinical milestones potentially due						550
Regulatory milestones potentially due						500
Sales-based milestones potentially due						$ 7,500
Clinical milestone expense	$ 0	$ 0	$ 0	$ 0
Clinical milestone payment	0	$ 0	0	$ 0
Accrued long-term liabilities
Agreements
Accrued milestone payments, noncurrent	$ 550		$ 550		$ 550