Note 5 - Investment Securities - Unrealized Gain (Loss) on Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Investment securities available for sale, at amortized cost	$ 380,948	$ 540,751
Investment securities available for sale, gross unrealized gains	5,252	2,548
Investment securities available for sale, gross unrealized losses	(3,979)	(4,257)
Investment securities available for sale, at fair value	382,221	539,042
Investment securities held to maturity, at amortized cost	556,159	644,842
Investment securities held to maturity, gross unrealized gains	27,047	9,867
Investment securities held to maturity, gross unrealized losses	(24)	(1,600)
Investment securities held to maturity, at fair value	583,182	653,109
US Government Agencies Debt Securities [Member]
Investment securities available for sale, at amortized cost	35,312	38,743
Investment securities available for sale, gross unrealized gains	0	1
Investment securities available for sale, gross unrealized losses	(216)	(439)
Investment securities available for sale, at fair value	35,096	38,305
Investment securities held to maturity, at amortized cost	87,958	94,913
Investment securities held to maturity, gross unrealized gains	4,731	482
Investment securities held to maturity, gross unrealized losses	0	(294)
Investment securities held to maturity, at fair value	92,689	95,101
Collateralized Mortgage Obligations [Member]
Investment securities available for sale, at amortized cost	224,578	329,492
Investment securities available for sale, gross unrealized gains	3,986	2,368
Investment securities available for sale, gross unrealized losses	(508)	(422)
Investment securities available for sale, at fair value	228,056	331,438
Investment securities held to maturity, at amortized cost	350,375	416,177
Investment securities held to maturity, gross unrealized gains	16,827	7,603
Investment securities held to maturity, gross unrealized losses	(23)	(793)
Investment securities held to maturity, at fair value	367,179	422,987
Agency Mortgage-backed Securities [Member]
Investment securities available for sale, at amortized cost	42,126	98,953
Investment securities available for sale, gross unrealized gains	946	82
Investment securities available for sale, gross unrealized losses	0	(98)
Investment securities available for sale, at fair value	43,072	98,937
Investment securities held to maturity, at amortized cost	117,826	133,752
Investment securities held to maturity, gross unrealized gains	5,489	1,782
Investment securities held to maturity, gross unrealized losses	(1)	(513)
Investment securities held to maturity, at fair value	123,314	135,021
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, at amortized cost	2,637	4,064
Investment securities available for sale, gross unrealized gains	28	18
Investment securities available for sale, gross unrealized losses	0	0
Investment securities available for sale, at fair value	2,665	4,082
Corporate Debt Securities [Member]
Investment securities available for sale, at amortized cost	76,295	69,499
Investment securities available for sale, gross unrealized gains	292	79
Investment securities available for sale, gross unrealized losses	(3,255)	(3,298)
Investment securities available for sale, at fair value	$ 73,332	$ 66,280

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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