Note 1 - Summary of Significant Accounting Policies - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred compensation plan assets	$ 38,858	$ 31,970
Deferred compensation plan liabilities	40,090	32,730
Other Long-term Assets [Member]
Deferred compensation plan assets	38,858	31,970
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	425	447
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	39,665	32,283
Cash Surrender Value [Member]
Deferred compensation plan assets	16,883	13,103
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 21,975	$ 18,867