Note 8 - Commitments and Off-Balance Sheet Risk - Exposure to Credit Losses (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Contractual amounts of financial instruments with off-balance sheet risk	$ 1,037,670,000	$ 1,036,775,000
Standby Letters of Credit [Member]
Contractual amounts of financial instruments with off-balance sheet risk	23,154,000	25,322,000
Unused lines of Credit [Member] | Commercial Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	759,338,000	784,895,000
Unused lines of Credit [Member] | One to Four Family Mortgages [Member]
Contractual amounts of financial instruments with off-balance sheet risk	57,030,000	57,378,000
Unused lines of Credit [Member] | Consumer Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	51,305,000	47,432,000
Unused lines of Credit [Member] | Consumer Other Financing Receivable 1 [Member]
Contractual amounts of financial instruments with off-balance sheet risk	20,253,000	20,231,000
Loan Origination Commitments [Member]
Contractual amounts of financial instruments with off-balance sheet risk	$ 126,590,000	$ 101,517,000