Note 11 - Retirement Fund and Profit Sharing Plan - Components of SERP Expense (Details) - Supplemental Employee Retirement Plan [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Service cost	$ 150	$ 144	$ 450	$ 432
Interest cost	159	185	477	555
Net amortization	86	48	258	144
Net periodic benefit cost	$ 395	$ 377	$ 1,185	$ 1,131