Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net loss	$ (7,659)	$ (9,778)
Denominator for basic and diluted EPS:
Weighted-average common shares outstanding (in shares)	36,140	31,896
Net loss per share attributable to common shareholders (basic and diluted) (in dollars per share)	$ (0.21)	$ (0.31)
Aggregate number of common equivalent shares (related to options, warrants and preferred stock) excluded from diluted net loss per common share (in shares)	6,200	5,000