Note 3 - Investment Securities Available for Sale - Amortized Cost and Estimated Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investment securities available for sale, amortized cost	$ 151,850	$ 156,410
Investment securities available for sale, gross unrealized gains	6,212	3,125
Investment securities available for sale, gross unrealized losses	(60)	(215)
Investment securities available for sale, Estimated fair value	158,002	159,320
Residential Mortgage Backed Securities Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, amortized cost	105,925	123,940
Investment securities available for sale, gross unrealized gains	4,086	1,924
Investment securities available for sale, gross unrealized losses	(2)	(186)
Investment securities available for sale, Estimated fair value	110,009	125,678
Commercial Mortgage Backed Securities Issued by US Government Agencies [Member]
Investment securities available for sale, amortized cost	5,400
Investment securities available for sale, gross unrealized gains	16
Investment securities available for sale, gross unrealized losses	0
Investment securities available for sale, Estimated fair value	5,416
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, amortized cost	40,525	32,470
Investment securities available for sale, gross unrealized gains	2,110	1,201
Investment securities available for sale, gross unrealized losses	(58)	(29)
Investment securities available for sale, Estimated fair value	$ 42,577	$ 33,642

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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