Note 7 - Derivatives and Hedging Activities - Hedged Interest Rate Swaps and Non-hedged Interest Rate Swaps (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Swapped loan portfolio loan-to-value percentage, including the potential swap exposure	65.00%
Interest rate swap
Derivative [Line Items]
Interest rate swaps collateralized by investment securities	$ 224,930	$ 98,555
Interest rate swap | Cash
Derivative [Line Items]
Interest rate swaps collateralized by investment securities	45,719
Interest rate swap | U.S. govt. sponsored agency securities
Derivative [Line Items]
Interest rate swaps collateralized by investment securities	3,628	3,541
Interest rate swap | Municipal securities
Derivative [Line Items]
Interest rate swaps collateralized by investment securities	85,937	22,924
Interest rate swap | Residential mortgage-backed and related securities
Derivative [Line Items]
Interest rate swaps collateralized by investment securities	$ 89,646	$ 72,090