Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total Revenue	$ 332	$ 349	$ 351	$ 693	$ 498	$ 546	$ 1,249	$ 277	$ 1,725	$ 2,570	$ 590
Operating expenses	6,271	6,299	6,823	5,107	8,833	5,685	6,667	3,549	24,500	24,734	13,811
Other income	21	22	24	31
Other income/(expense)					12	11	13	(333)	98	(297)	(671)
Net loss	$ (5,918)	$ (5,928)	$ (6,448)	$ (4,383)	$ (8,323)	$ (5,128)	$ (5,405)	$ (3,605)	$ (22,677)	$ (22,461)	$ (13,892)
Basic and diluted net loss per common share	$ (0.26)	$ (0.26)	$ (0.28)	$ (0.2)	$ (0.38)	$ (0.24)	$ (0.25)	$ (0.17)	$ (1)	$ (1.04)	$ (1.41)