CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Statement [Abstract]
Research and development revenue		$ 1,072		$ 2,299
Costs and expenses:
Research and development	$ 4,983	4,337	$ 10,177	8,535
General and administrative	1,866	1,887	3,940	3,931
Total costs and expenses	6,849	6,224	14,117	12,466
Loss from operations	(6,849)	(5,152)	(14,117)	(10,167)
Interest income	37	52	59	86
Interest expense	(389)		(719)
Net loss	(7,201)	(5,100)	(14,777)	(10,081)
Unrealized gain (loss) on marketable securities	(5)		(9)	29
Comprehensive loss	$ (7,206)	$ (5,100)	$ (14,786)	$ (10,052)
Basic and diluted net loss per share:
Net loss per share (in dollars per share)	$ (0.10)	$ (0.07)	$ (0.21)	$ (0.15)
Weighted average basic and diluted common shares outstanding (in shares)	71,149	71,062	71,143	68,275