Note 4 - Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Securities available for sale, amortized cost	$ 443,742	$ 577,406
Securities available-for-sale, unrealized gains	545	1,222
Securities available-for-sale, unrealized losses	(7,292)	(4,104)
Securities available-for-sale, fair value	436,995	574,524
US Government-sponsored Enterprises Debt Securities [Member]
Securities available for sale, amortized cost	264,234	214,852
Securities available-for-sale, unrealized gains	156	474
Securities available-for-sale, unrealized losses	(3,351)	(1,482)
Securities available-for-sale, fair value	261,039	213,844
US Treasury Securities [Member]
Securities available for sale, amortized cost		149,996
Securities available-for-sale, unrealized gains
Securities available-for-sale, unrealized losses		(12)
Securities available-for-sale, fair value		149,984
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available for sale, amortized cost	149,748	163,571
Securities available-for-sale, unrealized gains	282	383
Securities available-for-sale, unrealized losses	(3,753)	(2,447)
Securities available-for-sale, fair value	146,277	161,507
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale, amortized cost	29,760	48,987
Securities available-for-sale, unrealized gains	107	365
Securities available-for-sale, unrealized losses	(188)	(163)
Securities available-for-sale, fair value	$ 29,679	$ 49,189

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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