Note 10 - Interest and Other Income, Net - Interest and Other Income Components (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest income									$ 6,321	$ 5,353	$ 2,488
Amortization of premium on available-for-sale securities									(1,353)	(1,976)	(1,019)
Gain (loss) on deferred compensation plan investments									(1,022)	2,531	1,257
Foreign currency exchange gain (loss)									953	(550)	65
Other									95	162	26
Total	$ (393)	$ 2,714	$ 2,232	$ 440	$ 1,647	$ 1,255	$ 1,237	$ 1,381	$ 4,994	$ 5,520	$ 2,817