Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue
Operating expenses:
Research and development	20,472	13,931	11,917
General and administrative	14,000	8,883	4,526
Severance expense	3,010
Total operating expenses	37,482	22,814	16,443
Loss from operations	(37,482)	(22,814)	(16,443)
Other income (expense):
(Loss) gain on extinguishment of debt	(4,740)		1,900
Interest expense related to amortization of debt issuance costs and discount	(1,616)	(1,909)	(1,114)
Interest expense on principal	(5,511)	(2,671)	(1,605)
Fair value adjustment	32,465	(27,276)	(7,223)
Interest and other income	353	32	8
Total other income (expense)	20,951	(31,824)	(8,034)
Loss before income taxes	(16,531)	(54,638)	(24,477)
Income tax benefit (expense)	15	(26)	22
Net loss	$ (16,516)	$ (54,664)	$ (24,455)
Net loss per share:
Basic and diluted (in dollars per share)	$ (1.13)	$ (7.42)	$ (10.27)
Weighted average common shares outstanding:
Basic and diluted (in shares)	14,597,053	7,368,681	2,381,041