Note 9 - Fair Value Measurements and Disclosures (Details Textual)	3 Months Ended
	Mar. 31, 2020 USD ($) security issuer	Mar. 31, 2019 USD ($)
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Number of underlying issuers | issuer	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	0.0509
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
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