Note 3 - Available for Sale Debt Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Securities available-for-sale, less than 12 months, fair value	$ 723,776	$ 78,437
Securities available-for-sale, less than 12 months, unrealized losses	(10,466)	(279)
Securities available-for-sale, 12 months or more, fair value	0	25,319
Securities available-for-sale, 12 months or more, unrealized losses	0	(250)
Securities available-for-sale, fair value	723,776	103,756
Securities available-for-sale, unrealized losses	(10,466)	(529)
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	83,712
Securities available-for-sale, less than 12 months, unrealized losses	(204)
Securities available-for-sale, 12 months or more, fair value	0
Securities available-for-sale, 12 months or more, unrealized losses	0
Securities available-for-sale, fair value	83,712
Securities available-for-sale, unrealized losses	(204)
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	16,587	10,404
Securities available-for-sale, less than 12 months, unrealized losses	(68)	(112)
Securities available-for-sale, 12 months or more, fair value	0	24,398
Securities available-for-sale, 12 months or more, unrealized losses	0	(249)
Securities available-for-sale, fair value	16,587	34,802
Securities available-for-sale, unrealized losses	(68)	(361)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, less than 12 months, fair value	585,126	68,033
Securities available-for-sale, less than 12 months, unrealized losses	(9,698)	(167)
Securities available-for-sale, 12 months or more, fair value	0	921
Securities available-for-sale, 12 months or more, unrealized losses	0	(1)
Securities available-for-sale, fair value	585,126	68,954
Securities available-for-sale, unrealized losses	(9,698)	$ (168)
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	37,348
Securities available-for-sale, less than 12 months, unrealized losses	(493)
Securities available-for-sale, 12 months or more, fair value	0
Securities available-for-sale, 12 months or more, unrealized losses	0
Securities available-for-sale, fair value	37,348
Securities available-for-sale, unrealized losses	(493)
Other Debt Obligations [Member]
Securities available-for-sale, less than 12 months, fair value	1,003
Securities available-for-sale, less than 12 months, unrealized losses	(3)
Securities available-for-sale, 12 months or more, unrealized losses	0
Securities available-for-sale, fair value	1,003
Securities available-for-sale, unrealized losses	$ (3)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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