Note 1 - Summary of Significant Accounting Policies (Details Textual) - USD ($)			12 Months Ended
	Jul. 01, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018	Jul. 01, 2019
Cash, Uninsured Amount			$ 1,461,000	$ 4,507,000
Depreciation, Total			7,460,000	7,462,000
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Asset			$ 0
Standard Warranty Extended Term for Exceptions			10 years
Defined Contribution Plan, Cost			$ 1,333,000	1,195,000
Research and Development Expense, Total			$ 5,266,000	$ 5,952,000
Incremental Common Shares Attributable to Dilutive Effect of Contingently Issuable Shares			324,000	720,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	27.60%
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability		$ 3,323,000		$ 3,322,991
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance			$ 16,000
Accounting Standards Update 2014-09 [Member]
Cumulative Effect on Retained Earnings, Net of Tax, Total	$ 591,000
Other Expense [Member]
Foreign Currency Transaction Gain (Loss), before Tax, Total			$ (138,000)
Maximum [Member]
Finite-Lived Intangible Asset, Useful Life			20 years
Standard Warranty Term			5 years
Maximum [Member] | Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Operating Lease, Right-of-Use Asset					$ 12,500,000
Operating Lease, Liability, Total					12,500,000
Minimum [Member]
Finite-Lived Intangible Asset, Useful Life			7 years
Standard Warranty Term			1 year
Minimum [Member] | Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Operating Lease, Right-of-Use Asset					9,500,000
Operating Lease, Liability, Total					$ 9,500,000
Leasehold Improvements [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life			15 years