Note 1 - Summary of Significant Accounting Policies - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred compensation plan assets	$ 46,146	$ 38,858
Deferred compensation plan liabilities	48,435	40,090
Other Long-term Assets [Member]
Deferred compensation plan assets	46,146	38,858
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	155	425
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	48,280	39,665
Cash Surrender Value [Member]
Deferred compensation plan assets	19,222	16,883
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 26,924	$ 21,975