Note 11 - Deferred Compensation Plan - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Deferred compensation plan assets	$ 50,809	$ 46,146
Deferred compensation plan liabilities	53,081	48,435
Other Long-term Assets [Member]
Deferred compensation plan assets	50,809	46,146
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	396	155
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	52,685	48,280
Cash Surrender Value [Member]
Deferred compensation plan assets	21,013	19,222
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 29,796	$ 26,924