STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Collaboration revenue		$ 146	$ 6,389
Operating expenses:
Research and development	$ 38,331	34,134	45,084
General and administrative	19,527	19,918	14,798
Total operating expenses	57,858	54,052	59,882
Loss from operations	(57,858)	(53,906)	(53,493)
Other income, net	813	631	465
Non-cash inducement warrant expense	(60,751)
Change in fair value of derivative liabilities	0	158	(1,295)
Net loss	(117,796)	(53,117)	(54,323)
Preferred stock dividends		(16,998)	(18,938)
Settlement of a related party relationship		207,361
Net income (loss) applicable to common stockholders	$ (117,796)	$ 137,246	$ (73,261)
Net income (loss) per share - basic	$ (0.70)	$ 0.96	$ (0.53)
Net income (loss) per share - diluted	$ (0.70)	$ 0.96	$ (0.53)
Weighted average common shares outstanding used to compute basic net income (loss) per share	167,952,114	143,508,674	136,938,264
Weighted average common shares outstanding used to compute diluted net income (loss) per share	167,952,114	143,710,160	136,938,264