Note 4 - Balance Sheet Components - Other Long-term Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred compensation plan assets	$ 48,138	$ 46,146
Operating lease right-of-use (“ROU”) assets	5,845	3,719
Prepaid expense	2,503	2,340
Debt investment	2,820	2,861
Equity investment in a privately held company	3,180	3,400
Other	1,296	1,372
Total	$ 63,782	$ 59,838