Note 11 - Deferred Compensation Plan - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Deferred compensation plan assets	$ 35,547	$ 38,858
Deferred compensation plan liabilities	36,782	40,090
Other Long-term Assets [Member]
Deferred compensation plan assets	35,547	38,858
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	155	425
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	36,627	39,665
Cash Surrender Value [Member]
Deferred compensation plan assets	15,321	16,883
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 20,226	$ 21,975