Note 12 - Deferred Compensation Plan - Summary of Deferred Compensation Plan (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred compensation plan assets	$ 36,397	$ 31,970
Deferred compensation plan assets reported in:
Deferred compensation plan assets	36,397	31,970
Deferred compensation plan liabilities reported in:
Deferred compensation plan liabilities	37,393	32,730
Other Long-term Assets [Member]
Deferred compensation plan assets	36,397	31,970
Deferred compensation plan assets reported in:
Deferred compensation plan assets	36,397	31,970
Accrued Compensation and Related Benefits [Member]
Deferred compensation plan liabilities reported in:
Deferred compensation plan liabilities	425	447
Other Long-term Liabilities [Member]
Deferred compensation plan liabilities reported in:
Deferred compensation plan liabilities	36,968	32,283
Cash Surrender Value [Member]
Deferred compensation plan assets	16,429	13,103
Deferred compensation plan assets reported in:
Deferred compensation plan assets	16,429	13,103
Mutual Funds and Money Market Funds, Fair Value [Member]
Deferred compensation plan assets	19,968	18,867
Deferred compensation plan assets reported in:
Deferred compensation plan assets	$ 19,968	$ 18,867