Note 10 - Other Income, Net - Interest and Other Income Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest income	$ 9,327	$ 7,305	$ 6,321
Amortization of premium on available-for-sale securities	(2,979)	(729)	(1,353)
Gain (loss) on deferred compensation plan investments	4,592	3,806	(1,022)
Foreign currency exchange gain (loss)	(1,364)	(310)	953
Other	884	486	95
Total	$ 10,460	$ 10,558	$ 4,994