QUARTERLY FINANCIAL INFORMATION (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Table Text Block Supplement [Abstract]
License revenue	$ 38	$ 38	$ 38	$ 38	$ 38	$ 38	$ 38	$ 38
Total costs and expenses	37,998	60,899	35,582	34,727	54,188	34,366	44,383	41,615	$ 169,207	$ 174,552	$ 118,864
Net loss	$ (39,571)	$ (61,930)	$ (36,213)	$ (35,156)	$ (53,860)	$ (33,951)	$ (44,142)	$ (41,529)
Basic and diluted net loss per common share	$ (0.44)	$ (0.69)	$ (0.42)	$ (0.43)	$ (0.68)	$ (0.43)	$ (0.59)	$ (0.59)	$ (1.96)	$ (2.30)	$ (1.91)