Note 3 - Investment Securities Available for Sale - Amortized Cost and Estimated Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Investment securities available for sale, amortized cost	$ 153,083	$ 156,410
Investment securities available for sale, gross unrealized gains	6,165	3,125
Investment securities available for sale, gross unrealized losses	(1)	(215)
Investment securities available for sale, Estimated fair value	159,247	159,320
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, amortized cost	121,019	123,940
Investment securities available for sale, gross unrealized gains	4,876	1,924
Investment securities available for sale, gross unrealized losses		(186)
Investment securities available for sale, Estimated fair value	125,895	125,678
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, amortized cost	32,064	32,470
Investment securities available for sale, gross unrealized gains	1,289	1,201
Investment securities available for sale, gross unrealized losses	(1)	(29)
Investment securities available for sale, Estimated fair value	$ 33,352	$ 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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Amount, before tax, of unrealized loss 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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Amortized cost of 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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