Note 6 - Other Assets (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Surrender Value, Fair Value Disclosure	$ 14,700	$ 13,700
Increase (Decrease) in Cash Surrender Value	1,400	2,400
Investments Held in Rabbi Trust [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	700	1,100
Debt Securities, Available-for-sale, Total	700	1,100
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Benefit Obligation, Ending Balance	24,308	21,541	$ 18,676
Investments, Fair Value Disclosure, Total	$ 15,400	$ 14,700