Note 9 - Fair Value Measurements and Disclosures (Details Textual)	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($) security issuer	Sep. 30, 2019 USD ($) security issuer	Sep. 30, 2018 USD ($)
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of underlying issuers | issuer	3	3
Expected credit losses or prepayments		$ 0
Swap rate period		30 years
Measurement Input, Discount Rate [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Discount rate	0.0512	0.0512
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	$ 0
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
Maximum [Member] | London Interbank Offered Rate (LIBOR) [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