Note 1 - Significant Accounting Policies and Related Matters - Allowance for Doubtful Accounts and Sales Returns (Details) - Allowance for Doubtful Accounts and Sales Returns [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance	$ 522	$ 399	$ 349
Additions (recoveries) charged to income	293	388	264
Deductions from reserves	192	265	214
Balance	$ 623	$ 522	$ 399