PREPAID EXPENSES AND OTHER CURRENT ASSETS (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
PREPAID EXPENSES AND OTHER CURRENT ASSETS
Prepaid research and development expenses	$ 3,925	$ 2,349
Insurance premium asset	2,733	1,463
Prepaid rent expenses	74	108
Prepaid insurance expenses	86	91
Prepaid commercial and patient advocacy	523	968
Research and development tax credit receivable	279	500
Interest receivable	48	5
Other prepaid expenses and current assets	473	280
Total prepaid expenses & other current assets	$ 8,141	$ 5,764