Note 2 - Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Securities available for sale, amortized cost	$ 357,407	$ 317,528
Investment securities available for sale, at fair value	364,296	315,580
Total investment securities,, held to maturity, amortized cost		317,528
Total mortgage-backed securities, held to maturity, fair value		315,580
Collateralized Mortgage Backed Securities [Member]
Due within one year, amortized cost	80
Due within one year, estimated fair value	84
Due within one year, held to maturity, amortized cost		0
Due within one year, held to maturity, fair value		0
Due after one through five years, amortized cost	12,446
Due after one through five years, estimated fair value	12,402
Due after one through five years, held to maturity, amortized cost		13,360
Due after one through five years, held to maturity, fair value		13,391
Due after five through ten years, amortized cost	0
Due after five through ten years, estimated fair value	0
Due after five through ten years, held to maturity, amortized cost		6,261
Due after five through ten years, held to maturity, fair value		6,257
Due after ten years, amortized cost	75,791
Due after ten years, estimated fair value	76,774
Due after ten years, held to maturity, amortized cost		148,450
Due after ten years, held to maturity, fair value		148,835
Securities available for sale, amortized cost	88,317
Investment securities available for sale, at fair value	89,260
Total investment securities,, held to maturity, amortized cost		168,071
Total mortgage-backed securities, held to maturity, fair value		168,483
Investment Securities, Excluding Mortgage Backed Securities [Member]
Due within one year, amortized cost	0
Due within one year, estimated fair value	0
Due within one year, held to maturity, amortized cost		0
Due within one year, held to maturity, fair value		0
Due after one through five years, amortized cost	2,210
Due after one through five years, estimated fair value	2,328
Due after one through five years, held to maturity, amortized cost		2,043
Due after one through five years, held to maturity, fair value		2,084
Due after five through ten years, amortized cost	74,568
Due after five through ten years, estimated fair value	74,351
Due after five through ten years, held to maturity, amortized cost		58,460
Due after five through ten years, held to maturity, fair value		57,680
Due after ten years, amortized cost	192,312
Due after ten years, estimated fair value	198,357
Due after ten years, held to maturity, amortized cost		88,954
Due after ten years, held to maturity, fair value		87,333
Securities available for sale, amortized cost	269,090
Investment securities available for sale, at fair value	$ 275,036
Total investment securities,, held to maturity, amortized cost		149,457
Total mortgage-backed securities, held to maturity, fair value		$ 147,097