Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating expenses:
Research and development	$ 4,048	$ 4,071
General and administrative	2,589	2,294
Total operating expenses	6,637	6,365
Loss from operations	(6,637)	(6,365)
Other income :
Investment income	105	92
Other income, net	1	192
Total other income	106	284
Net loss	(6,531)	(6,081)
Foreign currency translation adjustment	(2)	2
Unrealized gain on available-for-sale investments		8
Comprehensive loss	(6,533)	(6,071)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(6,531)	(6,081)
Net loss attributable to common stockholders	$ (6,531)	$ (6,081)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.34)	$ (0.34)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	19,255,042	17,674,729
Included in operating expenses, above, are the following amounts for non-cash stock-based compensation expense:
Allocated share-based compensation	$ 780	$ 821
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	255	267
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	$ 525	$ 554