Changes in Stockholders' Equity and Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017	Dec. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 217,693
Net loss for the six months ended June 30, 2018	$ (20,223)	$ (13,022)	(26,175)	$ (20,297)
Unrealized gain related to marketable securities, net of tax			2
Recognized loss on redemption of marketable securities, previously unrealized			(1)
Translation adjustments, net of tax			(540)
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of tax			5,040
Stock-based compensation related to stock options, ESPP and RSUs			7,200
Accounting method transition adjustment					$ 27,401
Ending balance	230,620		230,620
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			1,239
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of tax			17
Ending balance	1,256		1,256
Additional Paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			695,768
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of tax			5,023
Stock-based compensation related to stock options, ESPP and RSUs			7,200
Ending balance	707,991		707,991
Accumulated deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(477,862)
Net loss for the six months ended June 30, 2018			(26,175)
Accounting method transition adjustment					$ 27,401
Ending balance	(476,636)		(476,636)
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(1,452)
Unrealized gain related to marketable securities, net of tax			2
Recognized loss on redemption of marketable securities, previously unrealized			(1)
Translation adjustments, net of tax			(540)
Ending balance	$ (1,991)		$ (1,991)