LICENSE AGREEMENTS AND COMMITMENTS - MSK License Agreement (Details) - MSK License Agreement - USD ($) $ in Thousands		12 Months Ended
	Aug. 20, 2015	Dec. 31, 2019	Dec. 31, 2016	Dec. 31, 2018
Agreements
Issuance of common stock to strategic partner (in shares)	1,428,500
Annual minimum royalties payable from fifth anniversary	$ 80
Expensed minimum royalty payments			$ 1,200
Clinical milestones potentially due	2,450
Regulatory milestones potentially due	9,000
Sales-based milestones potentially due	$ 20,000
Milestone expenses		$ 75
Milestone payment		725
Accrued short-term liabilities
Agreements
Short-term accrued minimum royalties		29
Accrued milestone payments, current		225		$ 875
Accrued long-term liabilities
Agreements
Long-term accrued minimum royalties		1,171		1,200
Accrued milestone payments, noncurrent		$ 300		$ 300