Note 11 - Deferred Compensation Plan - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Deferred compensation plan assets	$ 39,456	$ 38,858
Deferred compensation plan liabilities	41,242	40,090
Other Long-term Assets [Member]
Deferred compensation plan assets	39,456	38,858
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	155	425
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	41,087	39,665
Cash Surrender Value [Member]
Deferred compensation plan assets	17,279	16,883
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 22,177	$ 21,975