Note 4 - Balance Sheet Components - Other Long-term Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Deferred compensation plan assets	$ 50,641	$ 46,146
Operating lease right-of-use (“ROU”) assets	6,292	3,719
Prepaid expense	2,256	2,340
Debt investment	2,501	2,861
Equity investment in a privately held company	3,215	3,400
Other	2,145	1,372
Total	$ 67,050	$ 59,838