Note 11 - Retirement Plans - Allocation of Plan Assets (Details)	Dec. 31, 2020	Dec. 31, 2019
Plan assets, percent	100.00%	100.00%
Insurance General Account [Member]
Plan assets, percent	15.00%	17.00%
Cash and Cash Equivalents [Member]
Plan assets, percent	3.00%	2.00%
Equity Securities [Member]
Plan assets, percent	48.00%	47.00%
Fixed Income Securities [Member]
Plan assets, percent	32.00%	32.00%
Real Estate [Member]
Plan assets, percent	2.00%	2.00%