Note 3 - Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Investment securities available for sale, amortized cost	$ 173,491	$ 174,370
Investment securities available for sale, gross unrealized gains	1,206	361
Investment securities available for sale, gross unrealized losses	(1,470)	(3,224)
Investment securities available for sale, Estimated fair value	173,227	171,507
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, amortized cost	132,756	135,059
Investment securities available for sale, gross unrealized gains	652	240
Investment securities available for sale, gross unrealized losses	(1,320)	(2,621)
Investment securities available for sale, Estimated fair value	132,088	132,678
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, amortized cost	40,735	39,311
Investment securities available for sale, gross unrealized gains	554	121
Investment securities available for sale, gross unrealized losses	(150)	(603)
Investment securities available for sale, Estimated fair value	$ 41,139	$ 38,829

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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