SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
U.S. treasury securities (included in short-term investments)		$ 2,000
Level 1
Assets:
Money market funds (included in cash and cash equivalents)	$ 36,896	25,263
U.S. treasury securities (included in short-term investments)	0	1,999
Total assets	36,896	27,262
Liabilities:
Common Stock warrants (included in accrued and other liabilities)	0	0
Level 3
Assets:
Money market funds (included in cash and cash equivalents)	0	0
U.S. treasury securities (included in short-term investments)	0	0
Total assets	0	0
Liabilities:
Common Stock warrants (included in accrued and other liabilities)	$ 100	$ 100