Note 2 - Available for Sale Debt Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Available for sale debt securities, amortized cost	$ 675,478	$ 574,722
Securities available-for-sale, unrealized gains	7,048	12,785
Securities available-for-sale, unrealized losses	(10,359)	(529)
Securities available-for-sale, fair value	672,167	586,978
US Government-sponsored Enterprises Debt Securities [Member]
Available for sale debt securities, amortized cost	128,314	133,436
Securities available-for-sale, unrealized gains	2,758	5,003
Securities available-for-sale, unrealized losses	(348)	(361)
Securities available-for-sale, fair value	130,724	138,078
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available for sale debt securities, amortized cost	528,586	430,198
Securities available-for-sale, unrealized gains	4,140	7,555
Securities available-for-sale, unrealized losses	(9,595)	(168)
Securities available-for-sale, fair value	523,131	437,585
US States and Political Subdivisions Debt Securities [Member]
Available for sale debt securities, amortized cost	18,578	11,088
Securities available-for-sale, unrealized gains	150	227
Securities available-for-sale, unrealized losses	(416)	0
Securities available-for-sale, fair value	$ 18,312	$ 11,315

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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