Note 1 - Summary of Significant Accounting Policies - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred compensation plan assets	$ 31,970	$ 28,080
Deferred compensation plan liabilities	32,730	28,443
Other Long-term Assets [Member]
Deferred compensation plan assets	31,970	28,080
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	447	356
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	32,283	28,087
Cash Surrender Value [Member]
Deferred compensation plan assets	13,103	11,455
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 18,867	$ 16,625