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] 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]	Noncontrolling Interest [Member]	Total
Balance (Accounting Standards Update 2014-09 [Member]) at Dec. 30, 2017	[1]	$ 0	$ 0	$ 1,057	$ 0	$ 0	$ 1,057
Balance at Dec. 30, 2017								$ 28,489	$ 127,663	$ 150,726	$ (17,787)	$ 0	$ 289,091
Net income (loss)								0	0	(32,424)	0	0	(32,424)
Changes in cumulative translation adjustment								0	0	0			(8,905)
Changes in cumulative translation adjustment, attributable to parent											(8,905)		(8,905)
Changes in cumulative translation adjustment, attributable to non-controlling interest												0
Adjustments related to postretirement benefits, net of tax								0	0	0	805	0	805
Changes in unrealized gains and losses on investments, net of tax								0	0	0	7	0	7
Cash dividends								0	0	(7,689)	0	0	(7,689)
Exercise of stock options								67	613	0	0	0	680
Shares issued under ESPP								85	1,438	0	0	0	1,523
Shares issued for restricted stock units vested								541	(541)	0	0	0	0
Repurchase and retirement of stock								(195)	(11,405)	0	0	0	(11,600)
Noncontrolling interest								0	0	0	0	(299)	(299)
Share-based compensation expense								0	18,280	0	0	0	18,280
Shares issued for acquisition of Xcerra								11,776	283,642	0	0	0	295,418
Balance (Accounting Standards Update 2016-02 [Member]) at Dec. 29, 2018	[2]	$ 0	$ 0	$ 10,352	$ 0	$ 0	$ 10,352
Balance at Dec. 29, 2018								40,763	419,690	111,670	(25,880)	(299)	545,944
Net income (loss)								0	0	(69,692)	0	0	(69,692)
Changes in cumulative translation adjustment								0	0	0			(7,526)
Changes in cumulative translation adjustment, attributable to parent											(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	(628)
Changes in unrealized gains and losses on investments, net of tax													0
Cash dividends								0	0	(9,866)	0	0	(9,866)
Exercise of stock options								42	367	0	0	0	409
Shares issued under ESPP								187	2,159	0	0	0	2,346
Shares issued for restricted stock units vested								599	(599)	0	0	0	0
Repurchase and retirement of stock								(196)	(2,575)	0	0	0	(2,771)
Noncontrolling interest								0	0	53	0	(53)	0
Share-based compensation expense								0	14,148	0	0	0	14,148
Divestiture of interest in consolidated entity								0	0	0	0	356	356
Balance at Dec. 28, 2019								41,395	433,190	42,517	(34,030)	0	483,072
Net income (loss)								0	0	(13,801)	0	0	(13,801)
Changes in cumulative translation adjustment								0	0	0			27,321
Changes in cumulative translation adjustment, attributable to parent											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	2,383
Changes in unrealized gains and losses on investments, net of tax													0
Cash dividends								0	0	(2,486)	0	0	(2,486)
Exercise of stock options								101	1,001	0	0	0	1,102
Shares issued under ESPP								243	3,026	0	0	0	3,269
Shares issued for restricted stock units vested								660	(660)	0	0	0	0
Repurchase and retirement of stock								(209)	(2,597)	0	0	0	(2,806)
Share-based compensation expense								0	14,234	0	0	0	14,234
Balance at Dec. 26, 2020								$ 42,190	$ 448,194	$ 26,230	$ (4,326)	$ 0	$ 512,288

[1] Cumulative effect of accounting change relates to our adoption of ASU 2014-09.

[2] Cumulative effect of accounting change relates to our adoption of ASU 2016-02. Please refer to Note 1 of the Consolidated Financial Statements for further detail on the adoption of this accounting standard.