Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands		3 Months Ended			9 Months Ended			12 Months Ended
	Oct. 01, 2017 USD ($)	Sep. 29, 2018 USD ($) shares		Sep. 30, 2017 USD ($) shares	Sep. 29, 2018 USD ($) shares		Sep. 30, 2017 USD ($) shares	Dec. 26, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 30, 2017 USD ($)
Allowance for Doubtful Accounts Receivable, Current, Ending Balance		$ 200			$ 200					$ 200
Number of Operating Segments					1
Goodwill and Intangible Asset Impairment, Total	$ 0
Foreign Currency Transaction Gain (Loss), Realized		$ (200)		$ (200)	$ 1,200		$ (2,700)
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares		0		5,000	12,000		103,000
Contract with Customer, Liability, Total		$ 0		$ 0	$ 0		$ 0			0
Deferred Revenue		3,600			3,600					10,400
Deferred Profit		1,894	[1]		1,894	[1]			$ 5,350	6,608
Accumulated Other Comprehensive Income (Loss), Net of Tax, Total		(21,198)			(21,198)					(17,787)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss) Arising During Period, Net of Tax					0		0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total					0		0
Capitalized Computer Software, Net, Ending Balance		1,500			1,500
Contract with Customer, Asset, Net, Total		0		$ 0	0		$ 0			0
Broadcast Microwave Services, Inc. (“BMS”) [Member]
Proceeds from Divestiture of Businesses								$ 4,900
Disposal Group, Including Discontinued Operation, Contingent Consideration								$ 2,500
Non-current Other Accrued Liabilities [Member]
Deferred Profit Recognized After Year One		1,100			1,100					$ 800
Other Current Assets [Member]
Capitalized Computer Software, Net, Ending Balance		300			300
Other Noncurrent Assets [Member]
Capitalized Computer Software, Net, Ending Balance		$ 1,200			$ 1,200
Accounting Standards Update 2014-09 [Member]
Deferred Profit									(1,258)
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption									$ 1,100
Building [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life					30 years
Building [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life					40 years
Building Improvements [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life					5 years
Building Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life					15 years
Machinery, Equipment and Software [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life					3 years
Machinery, Equipment and Software [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life					10 years

[1] Balance sheet line items include the cumulative-effect adjustment recorded on December 31, 2017.