Note 6 - Other Assets (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Surrender Value, Fair Value Disclosure	$ 13,700	$ 11,600
Increase (Decrease) in Cash Surrender Value	2,400	(400)
Investments Held in Rabbi Trust [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	1,100	1,400
Debt Securities, Available-for-sale, Total	1,100	1,400
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Benefit Obligation, Ending Balance	21,541	18,676	$ 19,134
Investments, Fair Value Disclosure, Total	$ 14,700	$ 13,000