Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating expenses:
Research and development	$ 4,071	$ 4,246
General and administrative	2,294	2,234
Total operating expenses	6,365	6,480
Loss from operations	(6,365)	(6,480)
Other income (expense):
Investment income	92	32
Other income (expense), net	192	(50)
Total other income (expense)	284	(18)
Net loss	(6,081)	(6,498)
Foreign currency translation adjustment	2	0
Unrealized gain on available-for-sale investments	8
Comprehensive loss	(6,071)	(6,498)
Net loss attributable to common stockholders	$ (6,081)	$ (6,498)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.34)	$ (0.39)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	17,674,729	16,636,201
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 821	$ 845
Research and Development Expense [Member]
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	267	298
General and Administrative Expense [Member]
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 554	$ 547