LICENSE AGREEMENTS AND COMMITMENTS - MSK License Agreement (Details) - MSK License Agreement - USD ($) $ in Thousands		3 Months Ended			9 Months Ended		12 Months Ended
	Aug. 20, 2015	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	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
Clinical milestone expense		$ 0		$ 0	$ 0	$ 0
Milestone payment			$ 725
Accrued short-term liabilities
Agreements
Short-term accrued minimum royalties		18			18
Accrued milestone payments, current		150			150			$ 875
Accrued long-term liabilities
Agreements
Long-term accrued minimum royalties		1,182			1,182
Accrued milestone payments, noncurrent		$ 300			$ 300			$ 300