Note 2 - Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Total investment securities, amortized cost	$ 365,079	$ 317,528
Total investment securities, estimated fair value	369,111	315,580
Collateralized Mortgage Backed Securities [Member]
Due within one year, amortized cost	0	0
Due within one year, estimated fair value	0	0
Due after one through five years, amortized cost	11,956	13,360
Due after one through five years, estimated fair value	12,175	13,391
Due after five through ten years, amortized cost	142	6,261
Due after five through ten years, estimated fair value	142	6,257
Due after ten years, amortized cost	94,483	148,450
Due after ten years, estimated fair value	96,192	148,835
Total investment securities, amortized cost	106,581	168,071
Total investment securities, estimated fair value	108,509	168,483
Investment Securities, Excluding Mortgage Backed Securities [Member]
Due within one year, amortized cost	0	0
Due within one year, estimated fair value	0	0
Due after one through five years, amortized cost	4,524	2,043
Due after one through five years, estimated fair value	4,563	2,084
Due after five through ten years, amortized cost	71,563	58,460
Due after five through ten years, estimated fair value	70,390	57,680
Due after ten years, amortized cost	182,411	88,954
Due after ten years, estimated fair value	185,649	87,333
Total investment securities, amortized cost	258,498	149,457
Total investment securities, estimated fair value	$ 260,602	$ 147,097