Note 3 - Investment Securities - Amortized Cost and Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Securities held to maturity:
Securities held to maturity, at amortized cost	$ 476,165	$ 400,646
Securities held to maturity, gross unrealized gains	45,360	26,042
Securities held to maturity, gross unrealized (losses)	(248)	(143)
Securities held to maturity, fair value	521,277	426,545
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	350,060	206,962
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	12,430	4,068
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(524)	(335)
Debt Securities, Available-for-sale	361,966	210,695
Municipal securities
Securities held to maturity:
Securities held to maturity, at amortized cost	475,115	399,596
Securities held to maturity, gross unrealized gains	45,360	26,042
Securities held to maturity, gross unrealized (losses)	(248)	(143)
Securities held to maturity, fair value	520,227	425,495
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	147,241	46,659
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5,215	1,602
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(48)	(4)
Debt Securities, Available-for-sale	152,408	48,257
U.S. govt. sponsored agency securities
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	14,936	19,872
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	447	283
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(47)	(77)
Debt Securities, Available-for-sale	15,336	20,078
Residential mortgage-backed and related securities
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	127,670	118,724
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	5,510	2,045
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(338)	(182)
Debt Securities, Available-for-sale	132,842	120,587
Asset-backed securities
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	39,663	16,958
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	1,111
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	(91)	(71)
Debt Securities, Available-for-sale	40,683	16,887
Other Securities
Securities held to maturity:
Securities held to maturity, at amortized cost	1,050	1,050
Securities held to maturity, fair value	1,050	1,050
Securities available for sale:
Debt Securities, Available-for-sale, Amortized Cost	20,550	4,749
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	147	138
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax		(1)
Debt Securities, Available-for-sale	$ 20,697	$ 4,886

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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