Note 3 - Investment Securities - Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Securities held to maturity:
Securities held to maturity, at amortized cost	$ 400,646	$ 401,913
Securities held to maturity, gross unrealized gains	26,042	5,661
Securities held to maturity, gross unrealized (losses)	(143)	(6,804)
Securities held to maturity, fair value	426,545	400,770
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	206,962	266,671
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	4,068	501
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(335)	(6,116)
Debt Securities, Available-for-sale	210,695	261,056
US States and Political Subdivisions Debt Securities
Securities held to maturity:
Securities held to maturity, at amortized cost	399,596	400,863
Securities held to maturity, gross unrealized gains	26,042	5,661
Securities held to maturity, gross unrealized (losses)	(143)	(6,803)
Securities held to maturity, fair value	425,495	399,721
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	46,659	59,069
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,602	180
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(4)	(703)
Debt Securities, Available-for-sale	48,257	58,546
US Government Agencies Debt Securities
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	19,872	37,150
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	283	39
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(77)	(778)
Debt Securities, Available-for-sale	20,078	36,411
Residential mortgage-backed and related securities
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	118,724	163,698
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	2,045	182
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(182)	(4,631)
Debt Securities, Available-for-sale	120,587	159,249
Other Securities
Securities held to maturity:
Securities held to maturity, at amortized cost	1,050	1,050
Securities held to maturity, gross unrealized (losses)		(1)
Securities held to maturity, fair value	1,050	1,049
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	21,707	6,754
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	138	100
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(72)	(4)
Debt Securities, Available-for-sale	$ 21,773	$ 6,850

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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