Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating expenses:
Research and development	$ 22,172	$ 20,019	$ 56,218	$ 39,800
General and administrative	5,496	5,499	11,065	10,726
Total operating expenses	27,668	25,518	67,283	50,526
Loss from operations	(27,668)	(25,518)	(67,283)	(50,526)
Other income (expense):
Interest expense	(829)	(800)	(1,641)	(1,591)
Other income (expense)	219	364	486	671
Loss on debt extinguishment		(696)		(696)
Total other income/ (expense), net	(610)	(1,132)	(1,155)	(1,616)
Net loss	(28,278)	(26,650)	(68,438)	(52,142)
Comprehensive loss:
Net loss	(28,278)	(26,650)	(68,438)	(52,142)
Net unrealized gain (loss) on investment securities	7	47	31	312
Comprehensive loss	$ (28,271)	$ (26,603)	$ (68,407)	$ (51,830)
Net loss per share:
Net loss per share – basic and diluted	$ (0.56)	$ (0.70)	$ (1.49)	$ (1.48)
Weighted average shares outstanding – basic and diluted	50,062	38,198	45,918	35,271