Note 1 - Summary of Significant Accounting Policies - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred compensation plan assets	$ 28,080	$ 20,288
Deferred compensation plan liabilities	28,443	20,315
Other Long-term Assets [Member]
Deferred compensation plan assets	28,080	20,288
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	356	479
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	28,087	19,836
Cash Surrender Value [Member]
Deferred compensation plan assets	11,455	8,180
Mutual Funds, Fair Value [Member]
Deferred compensation plan assets	$ 16,625	$ 12,108