Description of Business and Basis of Presentation (Net Income (Loss) per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator
Net loss	$ (9,723)	$ (13,860)	$ (30,230)	$ (34,377)
Denominator
Basic and diluted (in shares)	42,497	37,008	39,381	34,929
Net loss per share
Basic and diluted (in dollars per share)	$ (0.23)	$ (0.37)	$ (0.77)	$ (0.98)