Note 3 - Loans and Allowance for Loan Losses - Retail Credit Exposure (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans	$ 3,216,358,000	$ 2,856,667,000	$ 2,753,085,000
Retail Portfolio Segment [Member]
Loans	422,396,000	415,123,000	$ 392,979,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Loans	61,620,000	75,374,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] | Performing Financial Instruments [Member]
Loans	61,378,000	75,119,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] | Nonperforming Financial Instruments [Member]
Loans	242,000	255,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Loans	360,776,000	339,749,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] | Performing Financial Instruments [Member]
Loans	358,447,000	337,856,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] | Nonperforming Financial Instruments [Member]
Loans	$ 2,329,000	$ 1,893,000