Net Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017	Sep. 29, 2018	Sep. 30, 2017
Numerator:
Net income (loss)	$ 809	$ (17,853)	$ (13,720)	$ (70,166)
Denominator:
Weighted-average common shares outstanding used to compute basic net income (loss) per share (in shares)	53,082	50,336	52,330	49,960
Effect of dilutive common stock equivalents (in shares	746	0	0	0
Weighted-average common shares outstanding used to compute diluted net income (loss) per share (in shares	53,828	50,336	52,330	49,960
Basic net income (loss) per common share (in dollars per share)	$ 0.02	$ (0.35)	$ (0.26)	$ (1.40)
Diluted net income (loss) per common share (in dollars per share)	$ 0.02	$ (0.35)	$ (0.26)	$ (1.40)
Potentially dilutive shares, weighted average (in shares)	2,513	5,741	6,032	5,704