Note 3 - Investment Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Securities held to maturity:
Securities held to maturity, less than 12 months, fair value	$ 1,059	$ 114,750
Securities held to maturity, less than 12 months, gross unrealized losses	(1)	(2,188)
Securities held to maturity, 12 months or more, fair value	10,047	69,412
Securities held to maturity, 12 months or more, gross unrealized losses	(142)	(4,616)
Securities held to maturity, fair value	11,106	184,162
Securities held to maturity, gross unrealized losses	(143)	(6,804)
Securities available for sale:
Securities available for sale, less than 12 months, fair value	20,829	46,980
Securities available for sale, less than 12 months, gross unrealized losses	(110)	(580)
Securities available for sale, 12 months or more, fair value	20,703	179,072
Securities available for sale, 12 months or more, gross unrealized losses	(225)	(5,536)
Securities available for sale, fair value	41,532	226,052
Securities available for sale, gross unrealized losses	(335)	(6,116)
US States and Political Subdivisions Debt Securities
Securities held to maturity:
Securities held to maturity, less than 12 months, fair value	509	114,201
Securities held to maturity, less than 12 months, gross unrealized losses	(1)	(2,187)
Securities held to maturity, 12 months or more, fair value	10,047	69,412
Securities held to maturity, 12 months or more, gross unrealized losses	(142)	(4,616)
Securities held to maturity, fair value	10,556	183,613
Securities held to maturity, gross unrealized losses	(143)	(6,803)
Securities available for sale:
Securities available for sale, less than 12 months, fair value	0	28,356
Securities available for sale, less than 12 months, gross unrealized losses	0	(394)
Securities available for sale, 12 months or more, fair value	724	15,932
Securities available for sale, 12 months or more, gross unrealized losses	(4)	(309)
Securities available for sale, fair value	724	44,288
Securities available for sale, gross unrealized losses	(4)	(703)
US Government Agencies Debt Securities
Securities available for sale:
Securities available for sale, less than 12 months, fair value	1,431	1,565
Securities available for sale, less than 12 months, gross unrealized losses	(21)	(34)
Securities available for sale, 12 months or more, fair value	2,117	29,605
Securities available for sale, 12 months or more, gross unrealized losses	(56)	(744)
Securities available for sale, fair value	3,548	31,170
Securities available for sale, gross unrealized losses	(77)	(778)
Residential mortgage-backed and related securities
Securities available for sale:
Securities available for sale, less than 12 months, fair value	2,263	12,810
Securities available for sale, less than 12 months, gross unrealized losses	(17)	(148)
Securities available for sale, 12 months or more, fair value	17,862	133,535
Securities available for sale, 12 months or more, gross unrealized losses	(165)	(4,483)
Securities available for sale, fair value	20,125	146,345
Securities available for sale, gross unrealized losses	(182)	(4,631)
Other Securities
Securities held to maturity:
Securities held to maturity, less than 12 months, fair value	550	549
Securities held to maturity, less than 12 months, gross unrealized losses		(1)
Securities held to maturity, fair value	550	549
Securities held to maturity, gross unrealized losses		(1)
Securities available for sale:
Securities available for sale, less than 12 months, fair value	17,135	4,249
Securities available for sale, less than 12 months, gross unrealized losses	(72)	(4)
Securities available for sale, 12 months or more, fair value	0
Securities available for sale, 12 months or more, gross unrealized losses	0
Securities available for sale, fair value	17,135	4,249
Securities available for sale, gross unrealized losses	$ (72)	$ (4)

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