STOCKHOLDERS’ DEFICIT - Reserve Shares of Common Stock (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Total common shares reserved for future issuance (in shares)	25,141,814	12,981,599
Outstanding stock options
Class of Stock [Line Items]
Total common shares reserved for future issuance (in shares)	8,781,615	7,117,002
Warrants to purchase common stock
Class of Stock [Line Items]
Total common shares reserved for future issuance (in shares)	14,040,452	1,914,316
Shares issuable upon conversion of convertible debt
Class of Stock [Line Items]
Total common shares reserved for future issuance (in shares)	1,217,008	1,720,224
For possible future issuance under the Omnibus Plan
Class of Stock [Line Items]
Total common shares reserved for future issuance (in shares)	1,102,739	2,230,057