Note 5 - Balance Sheet Components - Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred compensation plan liabilities	$ 48,280	$ 39,665
Dividend equivalents	7,871	6,265
Other	29	30
Total	57,873	47,063
Other Long-term Liabilities [Member]
Operating lease liabilities	$ 1,693	$ 1,103