Note 2 - Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance	$ 327	$ 256
Other than Temporary Impairment Losses, Investments, Total	0	0	$ 0
Inventory, Net, Total	9,819	9,422	9,748
Inventory Valuation Reserves, Ending Balance	508	468	571
Impairment of Long-Lived Assets Held-for-use	0	0	0
Capitalized Computer Software, Additions	0	0	0
Goodwill, Impairment Loss	0	0	0
Severance Costs	1,679	1,666	1,582
Financial Grants in Support of Research and Development	$ 1,678	$ 1,528	$ 2,687
Financial Grants in Support of Research and Development, Royalty Obligation	5.00%
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,317,197	1,378,282	334,833
Available-for-sale Securities, Amortized Cost Basis, Total	$ 112,885	$ 108,575
Available-for-sale Securities, Total	111,251	107,366
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax, Total	1,636	1,222
Allowance for Doubtful Accounts Receivable, Ending Balance	0	0
Cumulative Effect of New Accounting Principle in Period of Adoption		94
Accounting Standards Update 2016-02 [Member] | Subsequent Event [Member]
Operating Lease, Right-of-Use Asset				$ 12,500
Operating Lease, Liability, Total				$ 12,500
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption
Retained Earnings [Member] | Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption					$ 94
Foreign Exchange Option [Member]
Price Risk Cash Flow Hedge Asset, at Fair Value	$ 3,600	$ 0	$ 6,000
Minimum [Member]
Derivative Instrument Hedging Period	1 year
Maximum [Member]
Derivative Instrument Hedging Period		12 years
Debt Securities [Member]
Available-for-sale Securities, Amortized Cost Basis, Total	$ 99,406	$ 98,081
Available-for-sale Securities, Total	97,772	$ 96,872
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax, Total	$ 1,634