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]	Total
Balance at Dec. 28, 2019	$ 41,395	$ 433,190	$ 42,517	$ (34,030)	$ 483,072
Net income (loss)	0	0	(17,276)	0	(17,276)
Changes in cumulative translation adjustment	0	0	0	(929)	(929)
Cash dividends	0	0	(2,486)	0	(2,486)
Exercise of stock options	22	267	0	0	289
Shares issued for restricted stock units vested	403	(403)	0	0	0
Repurchase and retirement of stock	(134)	(1,263)	0	0	(1,397)
Share-based compensation expense	0	3,611	0	0	3,611
Adjustments related to postretirement benefits					0
Changes in unrealized gains and losses on investments, net of tax					0
Balance at Mar. 28, 2020	41,686	435,402	22,755	(34,959)	464,884
Balance at Dec. 26, 2020	42,190	448,194	26,230	(4,326)	512,288	[1]
Net income (loss)	0	0	27,607	0	27,607
Changes in cumulative translation adjustment	0	0	0	(10,246)	(10,246)
Exercise of stock options	192	1,730	0	0	1,922
Shares issued for restricted stock units vested	526	(526)	0	0	0
Repurchase and retirement of stock	(190)	(8,363)	0	0	(8,553)
Share-based compensation expense	0	3,523	0	0	3,523
Adjustments related to postretirement benefits	0	0	0	(180)	(180)
Changes in unrealized gains and losses on investments, net of tax	0	0	0	(6)	(6)
Sale of common stock, net of issuance costs	5,693	217,426	0	0	223,119
Balance at Mar. 27, 2021	$ 48,411	$ 661,984	$ 53,837	$ (14,758)	$ 749,474

[1] Derived from December 26, 2020 audited financial statements