Note 10 - Interest Income and Other Income, Net - Interest and Other Income Components (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income									$ 2,488	$ 1,608	$ 1,112
Amortization of premium on available-for-sale investments									(1,019)	(463)	(237)
Gain (loss) on employee deferred compensation plan investments									1,257	(375)	141
Foreign currency exchange gain									65	608	80
Other									26	43	(4)
Total	$ 897	$ 780	$ 597	$ 543	$ 550	$ (6)	$ 235	$ 642	$ 2,817	$ 1,421	$ 1,092