Note 3 - Available for Sale Debt Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Available for sale debt securities, amortized cost	$ 472,797	$ 469,313
Securities available-for-sale, unrealized gains	12,680	2,559
Securities available-for-sale, unrealized losses	(228)	(1,134)
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	485,249	470,738
US Treasury Securities [Member]
Available for sale debt securities, amortized cost	0	49,887
Securities available-for-sale, unrealized gains	0	10
Securities available-for-sale, unrealized losses	0	0
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	0	49,897
US Government-sponsored Enterprises Debt Securities [Member]
Available for sale debt securities, amortized cost	199,838	208,933
Securities available-for-sale, unrealized gains	4,788	1,189
Securities available-for-sale, unrealized losses	(215)	(178)
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	204,411	209,944
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available for sale debt securities, amortized cost	262,565	193,574
Securities available-for-sale, unrealized gains	7,702	1,243
Securities available-for-sale, unrealized losses	(13)	(956)
Securities available-for-sale, allowance for credit losses	0	0
Securities available-for-sale, fair value	270,254	193,861
US States and Political Subdivisions Debt Securities [Member]
Available for sale debt securities, amortized cost	10,394	16,919
Securities available-for-sale, unrealized gains	190	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	$ 10,584	$ 17,036

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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