SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Jan. 01, 2020 USD ($)
Property, Plant and Equipment [Line Items]
Available-for-sale securities, cost basis	$ 2,000,000	$ 29,900,000
U.S. treasury securities (included in short-term investments)	2,000,000	29,900,000
Unrealized loss		(3,000)
Impairment charges	0	0
Accumulated other comprehensive loss	0	(3,000)
Realized investment gains (losses)	0	0
Income tax penalties and interest expense	$ 0	$ 0
Number of operating segments | segment	1
Minimum
Property, Plant and Equipment [Line Items]
Estimated useful lives	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Subsequent event
Property, Plant and Equipment [Line Items]
Operating lease liability			$ 300,000
Right-of-use asset			$ 300,000