Note 4 - Balance Sheet Components - Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Deferred compensation plan liabilities	$ 41,087	$ 39,665
Dividend equivalents	6,787	6,265
Other	30	30
Total	49,801	47,063
Other Long-term Liabilities [Member]
Operating lease liabilities	$ 1,897	$ 1,103