Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balances (in shares) at Dec. 29, 2018	129,728,000
Balances at Dec. 29, 2018	$ 1,297	$ 736,274	$ (476,783)	$ (2,331)	$ 258,457
Net income	$ 0	0	29,506	0	29,506
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes (in shares)	3,774,000
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes	$ 38	8,327	0	0	8,365
Stock-based compensation related to stock options, ESPP and RSUs	0	13,335	0	0	13,335
Translation adjustments, net of tax	0	0	0	(7)	(7)
Change in actuarial valuation of defined benefit pension					0
Unrealized loss related to marketable securities, net of tax	0	0	0	42	42
Recognized gain on redemption of marketable securities, previously unrealized	$ 0	0	0	(53)	(53)
Balances (in shares) at Sep. 28, 2019	133,502,000
Balances at Sep. 28, 2019	$ 1,335	757,936	(447,277)	(2,349)	309,645
Balances (in shares) at Jun. 29, 2019	132,536,000
Balances at Jun. 29, 2019	$ 1,325	756,924	(460,816)	(2,256)	295,177
Net income	$ 0	0	13,539	0	13,539
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes (in shares)	966,000
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes	$ 10	(4,668)	0	0	(4,658)
Stock-based compensation related to stock options, ESPP and RSUs	0	5,680	0	0	5,680
Translation adjustments, net of tax	$ 0	0	0	(93)	(93)
Change in actuarial valuation of defined benefit pension					0
Unrealized loss related to marketable securities, net of tax					0
Recognized gain on redemption of marketable securities, previously unrealized					0
Balances (in shares) at Sep. 28, 2019	133,502,000
Balances at Sep. 28, 2019	$ 1,335	757,936	(447,277)	(2,349)	$ 309,645
Balances (in shares) at Dec. 28, 2019	133,883,000				133,883,000
Balances at Dec. 28, 2019	$ 1,339	762,213	(433,290)	(2,603)	$ 327,659
Net income	$ 0	0	31,403	0	31,403
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes (in shares)	2,195,000
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes	$ 22	(12,811)	0	0	(12,789)
Stock-based compensation related to stock options, ESPP and RSUs	0	30,228	0	0	30,228
Translation adjustments, net of tax	0	0	0	899	899
Change in actuarial valuation of defined benefit pension	$ 0	0	0	(507)	(507)
Unrealized loss related to marketable securities, net of tax					0
Recognized gain on redemption of marketable securities, previously unrealized					$ 0
Balances (in shares) at Sep. 26, 2020	136,078,000				136,078,000
Balances at Sep. 26, 2020	$ 1,361	779,630	(401,887)	(2,211)	$ 376,893
Balances (in shares) at Jun. 27, 2020	135,147,000
Balances at Jun. 27, 2020	$ 1,351	779,836	(414,494)	(2,563)	364,130
Net income	$ 0	0	12,607	0	12,607
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes (in shares)	931,000
Common stock issued in connection with the exercise of stock options, ESPP and vested RSUs, net of shares withheld for employee taxes	$ 10	(10,694)	0	0	(10,684)
Stock-based compensation related to stock options, ESPP and RSUs	0	10,488	0	0	10,488
Translation adjustments, net of tax	0	0	0	859	859
Change in actuarial valuation of defined benefit pension	$ 0	0	0	(507)	(507)
Unrealized loss related to marketable securities, net of tax					0
Recognized gain on redemption of marketable securities, previously unrealized					$ 0
Balances (in shares) at Sep. 26, 2020	136,078,000				136,078,000
Balances at Sep. 26, 2020	$ 1,361	$ 779,630	$ (401,887)	$ (2,211)	$ 376,893