Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Information [Abstract]
Operating expenses	$ 9,333	$ 8,201	$ 7,765	$ 6,360	$ 5,878	$ 5,970	$ 5,364	$ 4,469	$ 31,659	$ 21,681	$ 18,119
Net loss	$ (9,606)	$ (8,485)	$ (8,039)	$ (6,500)	$ (6,027)	$ (6,025)	$ (5,363)	$ (4,469)	$ (31,659)	$ (21,681)	$ (18,119)
Basic and Diluted (in dollars per share)	$ (0.63)	$ (0.55)	$ (8.07)	$ (13.14)	$ (14.20)	$ (13.55)	$ (13.42)	$ (11.29)	$ (4.06)	$ (51.56)	$ (47.80)
Basic and Diluted (in shares)	15,298,810	15,297,794	996,592	494,590	424,477	444,787	399,766	395,774	8,041,948	424,477	379,025