Note 13 - Selected Statements of Income Data - Financial Income, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income	$ 3,291	$ 4,220	$ 4,499
Loss on available-for-sale marketable securities, net	(6)	(28)	(67)
Amortization of premium on available-for-sale marketable securities, net	(444)	(554)	(773)
Foreign exchange gain (loss), net	443	(347)	(241)
Total	$ 3,284	$ 3,291	$ 3,418