Consolidated Statements of Stockholders' Equity - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]		Retained Earnings [Member]		AOCI Attributable to Parent [Member]	Total
Balance at Dec. 27, 2014	$ 25,692,000	$ 97,938,000		$ 134,152,000		$ (10,714,000)	$ 247,068,000
Net income				250,000			250,000
Changes in cumulative translation adjustment						(11,000,000)	(11,000,000)
Adjustments related to postretirement benefits, net of tax						(58,000)	(58,000)
Cash dividends - $0.24 per share				(6,249,000)			(6,249,000)
Exercise of stock options	175,000	1,335,000					1,510,000
Shares issued under ESPP	123,000	977,000					1,100,000
Shares issued for restricted stock units vested	377,000	(377,000)
Repurchase and retirement of stock	(127,000)	(1,250,000)					(1,377,000)
Share-based compensation expense		6,893,000					6,893,000
Changes in unrealized gains and losses on investments, net of tax
Balance at Dec. 26, 2015	26,240,000	105,516,000		128,153,000		(21,772,000)	238,137,000
Cumulative effect of accounting change (a) | Adjustments for New Accounting Principle, Early Adoption [Member]		249,000	[1]	(249,000)	[1]		200,000
Net income				3,039,000			3,039,000	[2]
Changes in cumulative translation adjustment						(5,789,000)	(5,789,000)
Adjustments related to postretirement benefits, net of tax						(316,000)	(316,000)
Cash dividends - $0.24 per share				(6,384,000)			(6,384,000)
Exercise of stock options	101,000	694,000					795,000
Shares issued under ESPP	111,000	959,000					1,070,000
Shares issued for restricted stock units vested	581,000	(581,000)
Repurchase and retirement of stock	(191,000)	(2,030,000)					(2,221,000)
Share-based compensation expense		7,143,000					7,143,000
Changes in unrealized gains and losses on investments, net of tax						(5,000)	(5,000)
Balance at Dec. 31, 2016	26,842,000	111,950,000		124,559,000		(27,882,000)	235,469,000
Cumulative effect of accounting change (a) | Adjustments for New Accounting Principle, Early Adoption [Member]				(200,000)
Net income				32,843,000			32,843,000
Changes in cumulative translation adjustment						11,345,000	11,345,000
Adjustments related to postretirement benefits, net of tax						(1,248,000)	(1,248,000)
Cash dividends - $0.24 per share				(6,676,000)			(6,676,000)
Exercise of stock options	1,164,000	11,617,000					12,781,000
Shares issued under ESPP	99,000	1,140,000					1,239,000
Shares issued for restricted stock units vested	595,000	(595,000)
Repurchase and retirement of stock	(211,000)	(3,456,000)					(3,667,000)
Share-based compensation expense		7,007,000					7,007,000
Changes in unrealized gains and losses on investments, net of tax						(2,000)	(2,000)
Balance at Dec. 30, 2017	$ 28,489,000	$ 127,663,000		$ 150,726,000		$ (17,787,000)	$ 289,091,000

[1] Cumulative effect of accounting change relates to our adoption of ASU 2016-09. Please refer to Note 1 of the Consolidated Financial Statements for further detail on the adoption of this accounting standard.

[2] As a result of the adoption of ASU 2016-09, in the fourth quarter of 2016, certain amounts in the first three quarters have been restated as if the new accounting guidance was adopted starting with the first day of our 2016 fiscal year. The impact of these restatements was not significant.