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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator
Net loss	$ (11,302)	$ (10,118)	$ (20,507)	$ (20,517)
Denominator
Basic and diluted (in shares)	38,068	35,526	37,797	33,871
Net loss per share
Basic and diluted (in dollars per share)	$ (0.30)	$ (0.28)	$ (0.54)	$ (0.61)