Note 3 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans - Ratios of Allowance for Loan Losses (Details)		3 Months Ended		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Ratio of allowance for loan losses to the end of period loans, net of unearned income and deferred fees and costs		0.99%	1.02%	0.94%
Ratio of net charge-offs to average loans, net of unearned income and deferred fees and costs(1)	[1]	0.06%	0.13%	0.09%

[1] Net charge-offs are on an annualized basis.