Note 3 - Available for Sale Debt Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Securities available for sale, amortized	$ 436,446	$ 469,313
Securities available-for-sale, unrealized gains	9,497	2,559
Securities available-for-sale, unrealized losses	(130)	(1,134)
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	445,813	470,738
US Government-sponsored Enterprises Debt Securities [Member]
Securities available for sale, amortized	203,401	208,933
Securities available-for-sale, unrealized gains	2,647	1,189
Securities available-for-sale, unrealized losses	(125)	(178)
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	205,923	209,944
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available for sale, amortized	219,811	193,574
Securities available-for-sale, unrealized gains	6,766	1,243
Securities available-for-sale, unrealized losses	(5)	(956)
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	226,572	193,861
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale, amortized	13,234	16,919
Securities available-for-sale, unrealized gains	84	117
Securities available-for-sale, unrealized losses	0	0
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	$ 13,318	17,036
US Treasury Securities [Member]
Securities available for sale, amortized		49,887
Securities available-for-sale, unrealized gains		10
Securities available-for-sale, unrealized losses		0
Securities available-for-sale, allowance for credit losses		0
Securities available-for-sale, fair value		$ 49,897

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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