Summary of Significant Accounting Policies (Net Loss Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss available for common shareholders - basic and diluted	$ (5,370)	$ (4,070)	$ (3,476)	$ (3,553)	$ (4,298)	$ (3,513)	$ (2,769)	$ (3,962)	$ (16,472)	$ (14,542)	$ (18,120)
Denominator:
Weighted-average shares outstanding - basic and diluted									51,958	46,540	41,599
Net loss per share - basic and diluted	$ (0.09)	$ (0.08)	$ (0.07)	$ (0.07)	$ (0.09)	$ (0.07)	$ (0.06)	$ (0.09)	$ (0.32)	$ (0.31)	$ (0.44)