Note 8 - Commitments and Off-balance Sheet Risk - Exposure to Credit Losses (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Contractual amounts of financial instruments with off-balance sheet risk	$ 958,204,000	$ 821,338,000
Standby Letters of Credit [Member]
Contractual amounts of financial instruments with off-balance sheet risk	26,956,000	26,202,000
Unused lines of Credit [Member] | Commercial Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	687,396,000	553,345,000
Unused lines of Credit [Member] | One to Four Family Mortgages [Member]
Contractual amounts of financial instruments with off-balance sheet risk	60,564,000	56,275,000
Unused lines of Credit [Member] | Consumer Portfolio Segment [Member]
Contractual amounts of financial instruments with off-balance sheet risk	37,258,000	22,689,000
Unused lines of Credit [Member] | Consumer Other Financing Receivable 1 [Member]
Contractual amounts of financial instruments with off-balance sheet risk	15,575,000	8,489,000
Loan Origination Commitments [Member]
Contractual amounts of financial instruments with off-balance sheet risk	$ 130,455,000	$ 154,338,000