BEIGENE AGREEMENT - Activity in Contract Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Movement in Deferred Revenue [Roll Forward]
Current deferred revenue	$ 371	$ 0
Noncurrent deferred revenue	100
Collaboration and License Agreement
Movement in Deferred Revenue [Roll Forward]
Opening balance at beginning of period	0
Revenue from performance obligations satisfied during reporting period	52
Payments received in advance	(533)
Closing balance at end of period	(481)
Current deferred revenue	400
Noncurrent deferred revenue	$ 100