STOCKHOLDERS' EQUITY (DEFICIT) - Warrants (Details) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	2,247
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	(853)
Warrants Expired (in shares)		0
Warrants outstanding, ending balance (in shares)	1,394
Warrants, Expiring June 2020
Warrant Or Right Outstanding [Roll Forward]
Exercise price (in dollars per share)	$ 1.47
Warrants outstanding, beginning balance (in shares)	0
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	0
Warrants Expired (in shares)		0
Warrants outstanding, ending balance (in shares)	0
Warrants, Expiring March 2023
Warrant Or Right Outstanding [Roll Forward]
Exercise price (in dollars per share)	$ 0.55
Warrants outstanding, beginning balance (in shares)	1,705
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	(378)
Warrants Expired (in shares)		0
Warrants outstanding, ending balance (in shares)	1,327
Warrants, Expiring November 2022
Warrant Or Right Outstanding [Roll Forward]
Exercise price (in dollars per share)	$ 0.55
Warrants outstanding, beginning balance (in shares)	487
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	(475)
Warrants Expired (in shares)		0
Warrants outstanding, ending balance (in shares)	12
Warrants, Expiring November 2024
Warrant Or Right Outstanding [Roll Forward]
Exercise price (in dollars per share)	$ 11.83
Warrants outstanding, beginning balance (in shares)	28
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	0
Warrants Expired (in shares)		0
Warrants outstanding, ending balance (in shares)	28
Warrants, Expiring November 2024
Warrant Or Right Outstanding [Roll Forward]
Exercise price (in dollars per share)	$ 11.04
Warrants outstanding, beginning balance (in shares)	27
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	0
Warrants Expired (in shares)		0
Warrants outstanding, ending balance (in shares)	27