Note 2 - Significant Accounting Policies (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	$ 256,000	$ 305,000
Other than Temporary Impairment Losses, Investments	0	0	$ 0
Inventory, Net	9,422,000	9,748,000	11,453,000
Inventory Valuation Reserves	468,000	571,000	670,000
Impairment of Long-Lived Assets Held-for-use	0	0	0
Capitalized Computer Software, Additions	0	0	1,086,000
Goodwill, Impairment Loss	0	0	0
Severance Costs	1,666,000	1,582,000	1,498,000
Financial Grants in Support of Research and Development	$ 1,528,000	$ 2,687,000	$ 2,738,000
Financial Grants in Support of Research and Development, Royalty Obligation	5.00%
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,378,282	334,833	403,632
Available-for-sale Securities, Amortized Cost Basis	$ 108,575,000	$ 108,225,000
Available-for-sale Securities	107,366,000	107,123,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1,222,000	1,152,000
Allowance for Doubtful Accounts Receivable	0	0
Subsequent Event [Member] | Accounting Standards Update 2014-09 [Member] | Liability [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 115,000
Subsequent Event [Member] | Accounting Standards Update 2014-09 [Member] | Assets [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption				21,000
Subsequent Event [Member] | Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 94,000
Foreign Exchange Option [Member]
Price Risk Cash Flow Hedge Asset, at Fair Value	0	6,000,000	$ 12,850,000
Foreign Exchange Forward Contracts and Put Options [Member]
Price Risk Cash Flow Hedge Asset, at Fair Value			$ 1,800,000
Debt Securities [Member]
Available-for-sale Securities, Amortized Cost Basis	98,081,000	100,615,000
Available-for-sale Securities	96,872,000	$ 99,513,000
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 1,209,000
Minimum [Member]
Finite-Lived Intangible Asset, Useful Life	5 years
Derivative Instrument Hedging Period	1 year
Maximum [Member]
Finite-Lived Intangible Asset, Useful Life	6 years
Derivative Instrument Hedging Period	1 year
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Asset, Useful Life	3 years