Note 2 - Acquisitions - Assets Acquired and Liabilities Assumed (Details) - USD ($)		9 Months Ended
	Oct. 01, 2015	Oct. 01, 2015	Dec. 31, 2017	Dec. 31, 2016
Consideration paid:
Goodwill			$ 40,196,000	$ 40,196,000
Acquisition of MNB [Member]
Consideration paid:
Cash	$ 28,000,000
Total consideration paid	70,000,000
Goodwill	14,500,000	$ 14,500,000	$ 14,500,000
Acquisition of MNB [Member] | Portion at Other than Fair Value Measurement [Member]
Assets acquired:
Cash and cash equivalents	14,069,000	14,069,000
Federal funds sold	51,000	51,000
Investment securities available for sale	42,677,000	42,677,000
Other investment securities, at cost	2,001,000	2,001,000
Loans receivable	375,521,000	375,521,000
Allowance for loan losses	(5,839,000)	(5,839,000)
Loans receivable, net	369,682,000	369,682,000
Accrued interest receivable	1,484,000	1,484,000
Real estate owned - net	97,000	97,000
Office properties and equipment, net	11,484,000	11,484,000
Cash surrender value of life insurance	6,202,000	6,202,000
Core deposit intangible
Deferred tax asset, net
Prepaid expenses and other assets	597,000	597,000
Total assets acquired	448,344,000	448,344,000
Liabilities assumed:
Deposits – noninterest bearing	56,187,000	56,187,000
Deposits – interest bearing	314,275,000	314,275,000
Total deposits	370,462,000	370,462,000
Short term borrowings	21,137,000	21,137,000
Other borrowings
Other liabilities	20,190,000	20,190,000
Total liabilities assumed	411,789,000	411,789,000
Net assets acquired	36,555,000	36,555,000
Acquisition of MNB [Member] | Changes Measurement [Member]
Assets acquired:
Cash and cash equivalents
Federal funds sold
Investment securities available for sale	88,000	88,000
Other investment securities, at cost
Loans receivable	(10,517,000)	(10,517,000)
Allowance for loan losses	5,839,000	5,839,000
Loans receivable, net	(4,678,000)	(4,678,000)
Accrued interest receivable
Real estate owned - net
Office properties and equipment, net	1,796,000	1,796,000
Cash surrender value of life insurance
Core deposit intangible	4,760,000	4,760,000
Deferred tax asset, net	144,000	144,000
Prepaid expenses and other assets
Total assets acquired	2,110,000	2,110,000
Liabilities assumed:
Deposits – noninterest bearing
Deposits – interest bearing	187,000	187,000
Total deposits	187,000	187,000
Short term borrowings
Other borrowings
Other liabilities	857,000	857,000
Total liabilities assumed	1,044,000	1,044,000
Net assets acquired	1,066,000	1,066,000
Acquisition of MNB [Member] | Estimate of Fair Value Measurement [Member]
Assets acquired:
Cash and cash equivalents	14,069,000	14,069,000
Federal funds sold	51,000	51,000
Investment securities available for sale	42,765,000	42,765,000
Other investment securities, at cost	2,001,000	2,001,000
Loans receivable	365,004,000	365,004,000
Allowance for loan losses
Loans receivable, net	365,004,000	365,004,000
Accrued interest receivable	1,484,000	1,484,000
Real estate owned - net	97,000	97,000
Office properties and equipment, net	13,280,000	13,280,000
Cash surrender value of life insurance	6,202,000	6,202,000
Core deposit intangible	4,760,000	4,760,000
Deferred tax asset, net	144,000	144,000
Prepaid expenses and other assets	597,000	597,000
Total assets acquired	450,454,000	450,454,000
Liabilities assumed:
Deposits – noninterest bearing	56,187,000	56,187,000
Deposits – interest bearing	314,462,000	314,462,000
Total deposits	370,649,000	370,649,000
Short term borrowings	21,137,000	21,137,000
Other borrowings
Other liabilities	21,047,000	21,047,000
Total liabilities assumed	412,833,000	412,833,000
Net assets acquired	37,621,000	37,621,000
Consideration paid:
Cash		10,100,000
Common stock		42,000,000
Total consideration paid		52,100,000
Goodwill	$ 14,479,000	$ 14,479,000