Note 12 - Deferred Compensation Plan - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Deferred compensation plan assets	$ 35,961	$ 31,970
Deferred compensation plan liabilities	37,019	32,730
Other Long-term Assets [Member]
Deferred compensation plan assets	35,961	31,970
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities	425	447
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities	36,594	32,283
Cash Surrender Value [Member]
Deferred compensation plan assets	14,644	13,103
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	$ 21,317	$ 18,867