Note 8 - Commitments and Off-Balance Sheet Risk - Exposure to Credit Losses (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Contractual amounts of financial instruments with off-balance sheet risk	$ 1,028,671,000	$ 1,012,197,000
Standby Letters of Credit [Member]
Contractual amounts of financial instruments with off-balance sheet risk	22,433,000	26,030,000
Unused lines of Credit [Member] | Commercial Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	730,070,000	682,202,000
Unused lines of Credit [Member] | One to Four Family Mortgages [Member]
Contractual amounts of financial instruments with off-balance sheet risk	57,680,000	61,606,000
Unused lines of Credit [Member] | Consumer Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	45,821,000	39,807,000
Unused lines of Credit [Member] | Consumer Other Financing Receivable 1 [Member]
Contractual amounts of financial instruments with off-balance sheet risk	20,972,000	17,629,000
Loan Origination Commitments [Member]
Contractual amounts of financial instruments with off-balance sheet risk	$ 151,695,000	$ 184,923,000