Note 3 - Investment Securities - Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Total, available for sale, amortized cost	$ 540,751	$ 326,740
Investment securities available for sale, gross unrealized gains	2,548	723
Investment securities available for sale, gross unrealized losses	(4,257)	(6,449)
Investment securities available for sale, at fair value	539,042	321,014
Investment securities available for sale, at amortized cost	540,751	326,740
Investment securities held to maturity, at amortized cost	644,842	761,563
Investment securities held to maturity, gross unrealized gains	9,867	570
Investment securities held to maturity, gross unrealized losses	(1,600)	(14,810)
Investment securities held to maturity, at fair value	653,109	747,323
US Government Agencies Debt Securities [Member]
Total, available for sale, amortized cost	38,743
Investment securities available for sale, gross unrealized gains	1
Investment securities available for sale, gross unrealized losses	(439)
Investment securities available for sale, at fair value	38,305
Investment securities available for sale, at amortized cost	38,743
Investment securities held to maturity, at amortized cost	94,913	107,390
Investment securities held to maturity, gross unrealized gains	482
Investment securities held to maturity, gross unrealized losses	(294)	(3,772)
Investment securities held to maturity, at fair value	95,101	103,618
Collateralized Mortgage Obligations [Member]
Total, available for sale, amortized cost	329,492	197,812
Investment securities available for sale, gross unrealized gains	2,368	567
Investment securities available for sale, gross unrealized losses	(422)	(2,120)
Investment securities available for sale, at fair value	331,438	196,259
Investment securities available for sale, at amortized cost	329,492	197,812
Investment securities held to maturity, at amortized cost	416,177	500,690
Investment securities held to maturity, gross unrealized gains	7,603	570
Investment securities held to maturity, gross unrealized losses	(793)	(5,793)
Investment securities held to maturity, at fair value	422,987	495,467
Agency Mortgage-backed Securities [Member]
Total, available for sale, amortized cost	98,953	39,105
Investment securities available for sale, gross unrealized gains	82	5
Investment securities available for sale, gross unrealized losses	(98)	(611)
Investment securities available for sale, at fair value	98,937	38,499
Investment securities available for sale, at amortized cost	98,953	39,105
Investment securities held to maturity, at amortized cost	133,752	153,483
Investment securities held to maturity, gross unrealized gains	1,782
Investment securities held to maturity, gross unrealized losses	(513)	(5,245)
Investment securities held to maturity, at fair value	135,021	148,238
US States and Political Subdivisions Debt Securities [Member]
Total, available for sale, amortized cost	4,064	20,807
Investment securities available for sale, gross unrealized gains	18	64
Investment securities available for sale, gross unrealized losses		(232)
Investment securities available for sale, at fair value	4,082	20,639
Investment securities available for sale, at amortized cost	4,064	20,807
Corporate Debt Securities [Member]
Total, available for sale, amortized cost	69,499	62,583
Investment securities available for sale, gross unrealized gains	79	87
Investment securities available for sale, gross unrealized losses	(3,298)	(3,396)
Investment securities available for sale, at fair value	66,280	59,274
Investment securities available for sale, at amortized cost	$ 69,499	62,583
Asset-backed Securities [Member]
Total, available for sale, amortized cost		6,433
Investment securities available for sale, gross unrealized gains
Investment securities available for sale, gross unrealized losses		(90)
Investment securities available for sale, at fair value		6,343
Investment securities available for sale, at amortized cost		$ 6,433

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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