Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands		Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]	Total
Changes in cumulative translation adjustment							$ (5,789)
Adjustments related to postretirement benefits, net of tax							(316)
Changes in unrealized gains and losses on investments, net of tax							(5)
Net loss from noncontrolling interest
Balance at Dec. 31, 2016		$ 26,842	$ 111,950	$ 124,559	$ (27,882)		235,469
Cumulative effect of accounting change (b) | Adjustments for New Accounting Principle, Early Adoption [Member]	[1]		249	(249)
Balance at Dec. 31, 2015		26,240	105,516	128,153	(21,772)		238,137
Cumulative effect of accounting change (a) (Adjustments for New Accounting Principle, Early Adoption [Member]) at Dec. 31, 2015	[1]		249	(249)
Net income				3,039			3,039
Changes in cumulative translation adjustment					(5,789)		(5,789)
Adjustments related to postretirement benefits, net of tax					(316)		(316)
Changes in unrealized gains and losses on investments, net of tax					(5)		(5)
Cash dividends - $0.24 per share				(6,384)			(6,384)
Exercise of stock options		101	694				795
Shares issued under ESPP		111	959				1,070
Shares issued for restricted stock units vested		581	(581)
Repurchase and retirement of stock		(191)	(2,030)				(2,221)
Share-based compensation expense			7,143				7,143
Cumulative effect of accounting change (b) | Adjustments for New Accounting Principle, Early Adoption [Member]	[1]		249	(249)
Net loss				3,039			3,039
Balance at Dec. 31, 2016		26,842	111,950	124,559	(27,882)		235,469
Net income				32,843			32,843
Changes in cumulative translation adjustment					11,345		11,345
Adjustments related to postretirement benefits, net of tax					(1,248)		(1,248)
Changes in unrealized gains and losses on investments, net of tax					(2)		(2)
Cash dividends - $0.24 per share				(6,676)			(6,676)
Exercise of stock options		1,164	11,617				12,781
Shares issued under ESPP		99	1,140				1,239
Shares issued for restricted stock units vested		595	(595)
Repurchase and retirement of stock		(211)	(3,456)				(3,667)
Share-based compensation expense			7,007				7,007
Net loss				32,843			32,843
Net loss from noncontrolling interest
Balance at Dec. 30, 2017		28,489	127,663	150,726	(17,787)		289,091
Cumulative effect of accounting change (b) | Adjustments for New Accounting Principle, Early Adoption [Member]	[2]			1,057			1,057
Cumulative effect of accounting change (a) (Adjustments for New Accounting Principle, Early Adoption [Member]) at Dec. 30, 2017	[2]			1,057			1,057
Net income				(32,424)			(32,424)
Changes in cumulative translation adjustment					(8,905)		(8,905)
Adjustments related to postretirement benefits, net of tax					805		805
Changes in unrealized gains and losses on investments, net of tax					7		7
Cash dividends - $0.24 per share				(7,689)			(7,689)
Exercise of stock options		67	613				680
Shares issued under ESPP		85	1,438				1,523
Shares issued for restricted stock units vested		541	(541)
Repurchase and retirement of stock		(195)	(11,405)				(11,600)
Share-based compensation expense			18,280				18,280
Cumulative effect of accounting change (b) | Adjustments for New Accounting Principle, Early Adoption [Member]	[2]			1,057			1,057
Net loss				(32,424)			(32,424)
Net loss from noncontrolling interest						(299)	(243)
Shares issued for acquisition of Xcerra		11,776	283,642				295,418
Balance at Dec. 29, 2018		$ 40,763	$ 419,690	$ 111,670	$ (25,880)	$ (299)	$ 545,944

[1] Cumulative effect of accounting change relates to our adoption of ASU 2016-09.

[2] Cumulative effect of accounting change relates to our adoption of ASU 2014-09. Please refer to Note 1 of the Consolidated Financial Statements for further detail on the adoption of this accounting standard.