Note 6 - Investment Securities (Details Textual)	3 Months Ended		12 Months Ended
	Mar. 31, 2017 USD ($) security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Investment Securities [Line Items]
Net (loss) gain on trading activities	$ 17,000	$ 34,000	$ (40,000)
Trading Securities, Change in Unrealized Holding Gain (Loss)	20,000		69,000
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	13,996,000	24,616,000
Available-for-sale Securities Pledged as Collateral	167,022,000		166,628,000
Income Tax Expense Benefit Related to Net Realized Gains Losses on Sales of Securities	254,000	108,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	0	0
Available-for-sale, amortized cost	387,489,000		396,168,000
Fair value	$ 382,296,000		390,475,000
Fair Value Inputs, Prepayment Rate	1.00%
Threshold For Identifying Banks With Trust Preferred Securities	$ 15,000,000,000
Minimum Cost Saving for Refinance	2.00%
Bank Failure Rate	0.37%
Fair Value Inputs, Loss Severity	95.00%
Collateralized Debt Obligations [Member]
Investment Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	$ 0	$ 0
Number Of Trust Preferred Securities | security	6
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year | security	5
Available-for-sale, amortized cost	$ 2,876,000		2,909,000
Fair value	$ 2,423,000		$ 2,281,000
Collateralized Debt Obligations [Member] | Minimum [Member]
Investment Securities [Line Items]
Fair Value Inputs, Probability of Default	0.23%
Fair Value Inputs, Loss Severity	0.00%
Collateralized Debt Obligations [Member] | Maximum [Member]
Investment Securities [Line Items]
Fair Value Inputs, Probability of Default	0.47%
Fair Value Inputs, Loss Severity	100.00%