Note 11 - Deferred Compensation Plan - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred compensation plan assets	$ 48,138	$ 46,146
Deferred compensation plan liabilities	50,233	48,435
Other Long-term Assets [Member]
Deferred compensation plan assets	48,138	46,146
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	396	155
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	49,837	48,280
Cash Surrender Value [Member]
Deferred compensation plan assets	19,886	19,222
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 28,252	$ 26,924