Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ 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	$ 3,891	$ 5,241	$ 8,137	$ 9,590
General and administrative	2,095	2,613	4,329	5,083
Total operating expenses	5,986	7,854	12,466	14,673
Loss from operations	(5,986)	(7,854)	(12,466)	(14,673)
Other income (expense):
Investment income	46	53	78	109
Other income (expense), net	332	(104)	282	107
Total other income (expense)	378	(51)	360	216
Net loss	(5,608)	(7,905)	(12,106)	(14,457)
Unrealized (loss) gain on available-for-sale investments	(7)	(2)	(7)	21
Comprehensive loss	(5,615)	(7,907)	(12,113)	(14,436)
Net loss attributable to common stockholders	$ (5,608)	$ (7,905)	$ (12,106)	$ (14,457)
Net loss per share attributable to common stockholders - basic and diluted (in dollars per share)	$ (0.33)	$ (0.48)	$ (0.72)	$ (0.87)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders - basic and diluted (in shares)	17,207,672	16,561,239	16,923,515	16,534,413
Included in operating expenses, above, are the following amounts for non-cash stock based compensation expense:
Allocated share-based compensation	$ 867	$ 946	$ 1,712	$ 1,812
Included in other (expense) income, net, above, are the following amounts from forward foreign currency contracts:
Realized losses from forward foreign currency contracts		(10)		(4)
Unrealized (losses) gains from forward foreign currency contracts		(53)		125
Total		(63)		121
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	308	321	606	629
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	$ 559	$ 625	$ 1,106	$ 1,183