Note 3 - Investment Securities - Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Securities held to maturity:
Securities held to maturity, due in one year or less, amortized cost	$ 2,636
Securities held to maturity, due in one year or less, fair value	2,651
Securities held to maturity, due after one year through five years, amortized cost	23,246
Securities held to maturity, due after one year through five years, fair value	23,800
Securities held to maturity, due after five years, amortized cost	446,701
Securities held to maturity, due after five years, fair value	495,846
Securities held to maturity, amortized cost	472,583
Securities held to maturity, fair value	522,297	$ 521,277
Securities available for sale:
Securities available for sale, due in one year or less, amortized cost	5,873
Securities available for sale, Due in one year or less, fair value	5,943
Securities available for sale, due after one year through five years, amortized cost	5,600
Securities available for sale, Due after one year through five years, fair value	5,764
Securities available for sale, due after five years, amortized cost	199,718
Securities available for sale, due after five years, fair value	204,676
Securities available for sale, single maturity, amortized cost	211,191
Securities available for sale, single maturity, fair value	216,383
Securities available for sale, amortized cost	329,994	350,060
Securities available for sale, fair value	337,830	361,966
Securities available for sale, callable, amortized cost	329,994
Securities available for sale, callable, fair value	337,830
Callable Securities [Member]
Securities available for sale:
Securities available for sale, amortized cost	182,830
Securities available for sale, fair value	187,859
Municipal securities.
Securities held to maturity:
Securities held to maturity, fair value	521,248	520,227
Securities available for sale:
Securities available for sale, amortized cost	163,253	147,241
Securities available for sale, fair value	168,266	152,408
Municipal securities. | Callable Securities [Member]
Securities held to maturity:
Securities held to maturity, callable, amortized cost	278,699
Securities held to maturity, callable, fair value	289,939
Securities available for sale:
Securities available for sale, callable, amortized cost	158,262
Securities available for sale, callable, fair value	163,070
Asset-backed securities
Securities available for sale:
Securities available for sale, amortized cost	26,372	39,663
Securities available for sale, fair value	27,124	40,683
Securities available for sale, callable, amortized cost	26,372
Securities available for sale, callable, fair value	27,124
Residential mortgage-backed and related securities
Securities available for sale:
Securities available for sale, amortized cost	92,431	127,670
Securities available for sale, fair value	94,323	132,842
Securities available for sale, callable, amortized cost	92,431
Securities available for sale, callable, fair value	94,323
Other Securities
Securities held to maturity:
Securities held to maturity, fair value	1,049	1,050
Securities available for sale:
Securities available for sale, amortized cost	24,568	20,550
Securities available for sale, fair value	24,789	$ 20,697
Other Securities | Callable Securities [Member]
Securities available for sale:
Securities available for sale, callable, amortized cost	24,568
Securities available for sale, callable, fair value	$ 24,789