Net Loss Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Numerator:
Net loss	$ (2,793)	$ (18,988)	$ (14,529)	$ (52,313)
Denominator:
Weighted-average common shares outstanding used to compute basic net loss per share (in shares)	52,290	50,019	51,952	49,772
Basic and diluted net loss per common share (in dollars per share)	$ (0.05)	$ (0.38)	$ (0.28)	$ (1.05)
Potentially dilutive shares, weighted average (in shares)	5,751	5,225	6,271	5,685