STOCKHOLDERS' (DEFICIT) EQUITY - Warrants (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2018	Nov. 01, 2017
Class of Warrant or Right [Line Items]
Exercise price per warrant (in dollars per share)		$ 1.47	$ 1.20	$ 0.80
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	9,258
Warrants Issued (in shares)	20,410
Warrants Exercised (in shares)	(6,773)
Warrants outstanding, ending balance (in shares)	22,895
Warrants, Expiring June 2020
Class of Warrant or Right [Line Items]
Exercise price per warrant (in dollars per share)	$ 1.47
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	0
Warrants Issued (in shares)	20,410
Warrants Exercised (in shares)	0
Warrants outstanding, ending balance (in shares)	20,410
Warrants, Expiring March 2023
Class of Warrant or Right [Line Items]
Exercise price per warrant (in dollars per share)	$ 0.95
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	7,211
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	(5,268)
Warrants outstanding, ending balance (in shares)	1,943
Warrants, Expiring November 2022
Class of Warrant or Right [Line Items]
Exercise price per warrant (in dollars per share)	$ 0.55
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	1,992
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	(1,505)
Warrants outstanding, ending balance (in shares)	487
Warrants, Expiring November 2024, Issued May 2015
Class of Warrant or Right [Line Items]
Exercise price per warrant (in dollars per share)	$ 11.83
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	28
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	0
Warrants outstanding, ending balance (in shares)	28
Warrants, Expiring November 2024, Issued November 2014
Class of Warrant or Right [Line Items]
Exercise price per warrant (in dollars per share)	$ 11.04
Warrant Or Right Outstanding [Roll Forward]
Warrants outstanding, beginning balance (in shares)	27
Warrants Issued (in shares)	0
Warrants Exercised (in shares)	0
Warrants outstanding, ending balance (in shares)	27