Basic and Diluted Net Income (Loss) Per Share - Earnings (Loss) Per Share Calculation (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
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)	$ (4,634)	$ (7,554)	$ (11,079)	$ (17,562)
Weighted average shares used to calculate net income (loss) per share, basic	39,493	38,966	39,424	38,840
Weighted average shares used to calculate net income (loss) per share, diluted	39,493	38,966	39,424	38,840
Basic (in dollars per share)	$ (0.12)	$ (0.19)	$ (0.28)	$ (0.45)
Diluted (in dollars per share)	$ (0.12)	$ (0.19)	$ (0.28)	$ (0.45)
Restricted Stock Units (RSUs) [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive equity awards	0	0	0	0
Stock Options [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Effect of dilutive equity awards	0	0	0	0