Note 13 - Selected Statements of Income Data - Financial Income, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest income	$ 4,220	$ 4,499	$ 4,233
Loss on available-for-sale marketable securities, net	(28)	(67)
Amortization of premium on available-for-sale marketable securities, net	(554)	(773)	(1,179)
Foreign exchange loss, net	(347)	(241)	(28)
Total	$ 3,291	$ 3,418	$ 3,026