Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] AOCI Attributable to Parent [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Treasury Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Noncontrolling Interest [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Treasury Stock [Member]	Noncontrolling Interest [Member]	Total
Balance (Accounting Standards Update 2016-02 [Member]) at Dec. 29, 2018	[1]	$ 0	$ 0	$ 10,352	$ 0	$ 0	$ 0	$ 10,352
Balance at Dec. 29, 2018									$ 40,763	$ 419,690	$ 111,670	$ (25,880)	$ 0	$ (299)	$ 545,944
Net income (loss)									0	0	(69,692)	0	0	0	(69,692)
Changes in cumulative translation adjustment									0	0	0		0		(7,526)
Foreign currency translation adjustments, net of tax												(7,522)			(7,522)
Changes in cumulative translation adjustment, attributable to non-controlling interest														(4)
Adjustments related to postretirement benefits, net of tax									0	0	0	(628)	0	0	(628)
Cash dividends									0	0	(9,866)	0	0	0	(9,866)
Exercise of stock options									42	367	0	0	0	0	409
Shares issued under ESPP									187	2,159	0	0	0	0	2,346
Shares issued for restricted stock units vested									599	(599)	0	0	0	0	0
Repurchase and retirement of stock									(196)	(2,575)	0	0	0	0	(2,771)
Noncontrolling interest									0	0	53	0	0	(53)	0
Share-based compensation expense									0	14,148	0	0	0	0	14,148
Divestiture of interest in consolidated entity									0	0	0	0	0	356	356
Changes in unrealized gains and losses on investments, net of tax															0
Balance at Dec. 28, 2019									41,395	433,190	42,517	(34,030)	0	0	483,072
Net income (loss)									0	0	(13,801)	0	0	0	(13,801)
Changes in cumulative translation adjustment									0	0	0		0		27,321
Foreign currency translation adjustments, net of tax												27,321			27,321
Changes in cumulative translation adjustment, attributable to non-controlling interest														0
Adjustments related to postretirement benefits, net of tax									0	0	0	2,383	0	0	2,383
Cash dividends									0	0	(2,486)	0	0	0	(2,486)
Exercise of stock options									101	1,001	0	0	0	0	1,102
Shares issued under ESPP									243	3,026	0	0	0	0	3,269
Shares issued for restricted stock units vested									660	(660)	0	0	0	0	0
Repurchase and retirement of stock									(209)	(2,597)	0	0	0	0	(2,806)
Share-based compensation expense									0	14,234	0	0	0	0	14,234
Changes in unrealized gains and losses on investments, net of tax															0
Balance at Dec. 26, 2020									42,190	448,194	26,230	(4,326)	0	0	512,288
Net income (loss)									0	0	167,325	0	0	0	167,325
Changes in cumulative translation adjustment									0	0	0		0		(22,956)
Foreign currency translation adjustments, net of tax												(22,956)			(22,956)
Changes in cumulative translation adjustment, attributable to non-controlling interest														0
Adjustments related to postretirement benefits, net of tax									0	0	0	2,602	0	0	2,602
Exercise of stock options									250	2,260	0	0	0	0	2,510
Shares issued under ESPP									161	3,403	0	0	0	0	3,564
Shares issued for restricted stock units vested									704	(704)	0	0	0	0	0
Repurchase and retirement of stock									(242)	(10,222)	0	0	0	0	(10,464)
Share-based compensation expense									0	14,420	0	0	0	0	14,420
Common stock repurchases									0	0	0	0	(7,324)	0	(7,324)
Changes in unrealized gains and losses on investments, net of tax									0	0	0	(67)	0	0	(67)
Impact of sale of PCB Test business									0	0	0	(2,515)	0	0	(2,515)
Sale of common stock, net of issuance costs									5,693	217,426	0	0	0	0	223,119
Balance at Dec. 25, 2021									$ 48,756	$ 674,777	$ 193,555	$ (27,262)	$ (7,324)	$ 0	$ 882,502

[1] Cumulative effect of accounting change relates to our adoption of ASU 2016-02.