Note 8 - Commitments and Off-balance Sheet Risk - Exposure to Credit Losses (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Contractual amounts of financial instruments with off-balance sheet risk	$ 1,361,418,000	$ 1,038,444,000
Standby Letters of Credit [Member]
Contractual amounts of financial instruments with off-balance sheet risk	20,018,000	22,798,000
Unused lines of Credit [Member] | Commercial Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	956,030,000	776,493,000
Unused lines of Credit [Member] | One to Four Family Mortgages [Member]
Contractual amounts of financial instruments with off-balance sheet risk	59,996,000	60,858,000
Unused lines of Credit [Member] | Consumer Credit Card [Member]
Contractual amounts of financial instruments with off-balance sheet risk	67,880,000	58,199,000
Unused lines of Credit [Member] | Consumer Other Financing Receivable 1 [Member]
Contractual amounts of financial instruments with off-balance sheet risk	25,599,000	18,135,000
Loan Origination Commitments [Member]
Contractual amounts of financial instruments with off-balance sheet risk	$ 231,895,000	$ 101,961,000