Net Loss Per Share (Computation of Loss Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (5,811)	$ (3,577)	$ (11,425)	$ (9,150)
Denominator:
Weighted-average common shares outstanding, basic and diluted (in shares)	17,778,184	16,269,808	17,374,789	15,851,106
Net loss per common share, basic and diluted (in USD per share)	$ (0.33)	$ (0.22)	$ (0.66)	$ (0.58)