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
Quarterly Financial Information Disclosure [Abstract]
Operating Expenses	$ 4,802	$ 10,640	$ 2,596	$ 2,629	$ 2,602	$ 2,662	$ 2,226	$ 1,043	$ 20,667	$ 8,533	$ 5,257
Interest income	89	7	2	6	5	5	(3)	9	104	16	21
Net loss	(4,714)	(10,632)	(2,594)	(2,623)	(2,597)	(2,657)	(2,229)	(1,034)	(20,563)	(8,517)	(5,236)
Net loss attributable to common stockholders	$ (4,927)	$ (11,652)	$ (3,270)	$ (3,280)	$ (3,258)	$ (3,136)	$ (2,693)	$ (1,484)	$ (23,129)	$ (10,571)	$ (6,976)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.28)	$ (5.12)	$ (1.52)	$ (1.61)	$ (1.76)	$ (1.75)	$ (1.61)	$ (0.95)	$ (3.79)	$ (6.15)	$ (6.45)