Changes in Stockholders' Equity and Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jul. 02, 2016	Jul. 01, 2017	Jul. 02, 2016	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			$ 270,430
Net loss for the six months ended July 1, 2017	$ (13,022)	$ (13,810)	(20,297)	$ (33,521)
Unrealized loss related to marketable securities, net of tax			(71)
Recognized loss on redemption of marketable securities, previously unrealized			200
Translation adjustments, net of tax			950
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of tax			1,183
Stock-based compensation expense related to stock options, ESPP and RSUs			6,772
Defined benefit pension, net of actuarial losses	(47)	$ 141	(47)	$ 141
Accounting method transition adjustment					$ (355)
Ending balance	258,765		258,765
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			1,216
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of tax			11
Ending balance	1,227		1,227
Additional Paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			680,315
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of tax			1,172
Stock-based compensation expense related to stock options, ESPP and RSUs			6,772
Ending balance	688,259		688,259
Accumulated deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(406,945)
Net loss for the six months ended July 1, 2017			(20,297)
Accounting method transition adjustment					$ (355)
Ending balance	(427,597)		(427,597)
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(4,156)
Unrealized loss related to marketable securities, net of tax			(71)
Recognized loss on redemption of marketable securities, previously unrealized			200
Translation adjustments, net of tax			950
Defined benefit pension, net of actuarial losses			(47)
Ending balance	$ (3,124)		$ (3,124)