Note 4 -Investment Securities (Details Textual)	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) security	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Investment Securities [Line Items]
Net (loss) gain on trading activities			$ 27,000	$ (40,000)	$ 33,000
Trading Securities, Change in Unrealized Holding Gain (Loss)				69,000
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds			42,509,000	32,573,000	47,960,000
Income Tax Expense Benefit Related to Net Realized Gains Losses on Sales of Securities			510,000	229,000	266,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses			0	0	0
Available-for-sale Securities Pledged as Collateral			202,887,000	166,628,000
(Gain) loss on sale of investments			(1,580,000)	(866,000)	(838,000)
Recorded OTTI credit loss			80,000	192,000	55,000
Non-interest Income [Member]
Investment Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities			80,000
Collateralized Debt Obligations [Member]
Investment Securities [Line Items]
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses			0	$ 0	$ 0
PreTSL IV [Member]
Investment Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities			$ 1,000
Number Of Trust Preferred Securities | security			1
Recorded OTTI credit loss			$ 1,000
PreTSL [Member]
Investment Securities [Line Items]
Non-performing securities sold | security	5
Carrying value of securities	$ 2,235,000	$ 2,235,000
Number of securities OTTI recorded | security	4
Recorded OTTI credit loss	$ 1,152,000
Amount of reduction in risk-based assets		$ 19,000,000
PreTSL [Member] | Non-interest Income [Member]
Investment Securities [Line Items]
(Gain) loss on sale of investments	$ 15,000