Condensed 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]	Noncontrolling Interest [Member]	Total
Balance at Dec. 30, 2017		$ 28,489	$ 127,663	$ 150,726	$ (17,787)		$ 289,091
Net income (loss)				24,573			24,573
Changes in cumulative translation adjustment					(3,435)		(3,435)
Adjustments related to postretirement benefits, net of tax					17		17
Cash dividends				(5,246)			(5,246)
Exercise of stock options		65	575				640
Shares issued for restricted stock units vested		473	(473)
Repurchase and retirement of stock		(167)	(3,788)				(3,955)
Share-based compensation expense			5,496				5,496
Cumulative effect of accounting change(a) at Dec. 30, 2017	[1]			1,057			1,057
Shares issued under ESPP		41	721				762
Changes in unrealized gains and losses on investments, net of tax					7		7
Balance at Sep. 29, 2018		28,901	130,194	171,110	(21,198)		309,007
Balance at Jun. 30, 2018		28,883	128,248	168,040	(20,708)		304,463
Net income (loss)				4,803			4,803
Changes in cumulative translation adjustment					(475)		(475)
Adjustments related to postretirement benefits, net of tax					(24)		(24)
Cash dividends				(1,733)			(1,733)
Exercise of stock options		15	111				126
Shares issued for restricted stock units vested		5	(5)
Repurchase and retirement of stock		(2)	(39)				(41)
Share-based compensation expense			1,879				1,879
Changes in unrealized gains and losses on investments, net of tax					9		9
Balance at Sep. 29, 2018		28,901	130,194	171,110	(21,198)		309,007
Balance at Dec. 29, 2018		40,763	419,690	111,670	(25,880)	(299)	545,944	[2]
Net income (loss)				(52,372)			(52,372)
Changes in cumulative translation adjustment					(14,850)	(4)	(14,854)
Adjustments related to postretirement benefits, net of tax					470		470
Cash dividends				(7,383)			(7,383)
Exercise of stock options		37	293				330
Shares issued for restricted stock units vested		597	(597)
Repurchase and retirement of stock		(196)	(2,562)				(2,758)
Share-based compensation expense			10,861				10,861
Cumulative effect of accounting change(a) at Dec. 29, 2018	[3]			10,352			10,352
Shares issued under ESPP		64	743				807
Noncontrolling interest				53		(53)
Changes in unrealized gains and losses on investments, net of tax
Balance at Sep. 28, 2019		41,265	428,428	62,320	(40,260)	(356)	491,397
Balance at Jun. 29, 2019		41,100	425,609	75,115	(27,019)	(356)	514,449
Net income (loss)				(10,326)			(10,326)
Changes in cumulative translation adjustment					(13,276)		(13,276)
Adjustments related to postretirement benefits, net of tax					35		35
Cash dividends				(2,469)			(2,469)
Exercise of stock options		22	186				208
Shares issued for restricted stock units vested		203	(203)
Repurchase and retirement of stock		(60)	(670)				(730)
Share-based compensation expense			3,506				3,506
Changes in unrealized gains and losses on investments, net of tax
Balance at Sep. 28, 2019		$ 41,265	$ 428,428	$ 62,320	$ (40,260)	$ (356)	$ 491,397

[1] Cumulative effect of accounting change relates to our adoption of ASU 2014-09, Revenue from Contracts with Customers (Topic 606).

[2] Derived from December 29, 2018 audited financial statements

[3] Cumulative effect of accounting change relates to our adoption of ASU 2016-02, Leases (Topic 842).