Note 3 - Loans and Allowance for Loan Losses - Retail Credit Exposure (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Loans	$ 3,350,544,000	$ 2,856,667,000
Retail Portfolio Segment [Member]
Loans	412,183,000	415,123,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Loans	63,723,000	75,374,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] | Performing Financial Instruments [Member]
Loans	63,458,000	75,119,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] | Nonperforming Financial Instruments [Member]
Loans	265,000	255,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Loans	348,460,000	339,749,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] | Performing Financial Instruments [Member]
Loans	346,266,000	337,856,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] | Nonperforming Financial Instruments [Member]
Loans	$ 2,194,000	$ 1,893,000