Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Operating expenses:
Research and development	$ 2,760	$ 3,891	$ 6,831	$ 8,137
General and administrative	2,240	2,095	4,534	4,329
Total operating expenses	5,000	5,986	11,365	12,466
Loss from operations	(5,000)	(5,986)	(11,365)	(12,466)
Other income:
Investment income	106	46	198	78
Other income, net	15	332	207	282
Total other income	121	378	405	360
Net loss	(4,879)	(5,608)	(10,960)	(12,106)
Foreign currency translation adjustment	(3)	0	(1)
Unrealized gain (loss) on available-for-sale investments	8	(7)	16	(7)
Comprehensive loss	(4,874)	(5,615)	(10,945)	(12,113)
Net loss attributable to common stockholders	$ (4,879)	$ (5,608)	$ (10,960)	$ (12,106)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.28)	$ (0.33)	$ (0.62)	$ (0.72)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	17,674,729	17,207,672	17,674,729	16,923,515
Included in operating expenses, above, are the following amounts for non-cash stock-based compensation expense:
Allocated share-based compensation	$ 922	$ 867	$ 1,743	$ 1,712
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	312	308	579	606
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	$ 610	$ 559	$ 1,164	$ 1,106