Note 3 - Loans and Allowance for Loan Losses - Retail Credit Exposure (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Loans	$ 2,901,543,000	$ 2,856,667,000
Retail Portfolio Segment [Member]
Loans	429,213,000	415,123,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member]
Loans	72,875,000	75,374,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] | Performing Financial Instruments [Member]
Loans	72,596,000	75,119,000
Retail Portfolio Segment [Member] | Home Equity and Other [Member] | Nonperforming Financial Instruments [Member]
Loans	279,000	255,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member]
Loans	356,338,000	339,749,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] | Performing Financial Instruments [Member]
Loans	353,918,000	337,856,000
Retail Portfolio Segment [Member] | One to Four Family Mortgages [Member] | Nonperforming Financial Instruments [Member]
Loans	$ 2,420,000	$ 1,893,000