Note 7 - Derivatives and Hedging Activities - Hedged Interest Rate Swaps and Non-hedged Interest Rate Swaps (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Interest rate swaps are collateralized by investment securities	$ 113,300	$ 100,900
Interest rate swap
Derivative [Line Items]
Interest rate swaps are collateralized by investment securities	98,555
Interest rate swap | U.S. govt. sponsored agency securities
Derivative [Line Items]
Interest rate swaps are collateralized by investment securities	3,541
Interest rate swap | Municipal securities
Derivative [Line Items]
Interest rate swaps are collateralized by investment securities	22,924
Interest rate swap | Residential mortgage-backed and related securities
Derivative [Line Items]
Interest rate swaps are collateralized by investment securities	72,090
Collateral Pledged | Interest rate swap
Derivative [Line Items]
Restricted cash	$ 10,000	$ 18,500