Note 9 - Fair Value Measurements and Disclosures (Details Textual)	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($) security issuer	Jun. 30, 2018 USD ($) security issuer	Jun. 30, 2017 USD ($)
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of underlying issuers | issuer	5	5
Expected credit losses or prepayments		$ 0
Swap rate period		30 years
Discount rate		5.74%
Fair Value, Inputs, Level 3 [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		$ 0	$ (15,000)
Fair Value, Inputs, Level 3 [Member] | Collateralized Debt Obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of trust preferred securities | security	1	1
London Interbank Offered Rate (LIBOR) [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	$ 0	$ 0