Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Numerator:
Net loss	$ (4,910)	$ (4,416)	$ (2,152)	$ (4,862)	$ (2,370)	$ (6,917)	$ (4,638)	$ (5,995)	$ (16,340)	$ (19,920)	$ (15,622)
Less: dividends accumulated on convertible preferred stock									6,736	6,005	5,352
Numerator of basic and diluted EPS									$ (23,076)	$ (25,925)	$ (20,974)
Denominator for basic and diluted EPS:
Weighted-average common shares outstanding									23,760	11,642	3,016
Net loss per share attributable to common shareholders (basic and diluted) (in dollars per share)	$ (0.28)	$ (0.26)	$ (0.16)	$ (0.27)	$ (0.17)	$ (0.82)	$ (0.94)	$ (1.26)	$ (0.97)	$ (2.23)	$ (6.95)
Aggregate number of common equivalent shares (related to options, warrants and preferred stock) that have been excluded from computations of diluted net loss per common share									6,700	2,300	2,400