Note 2 - Investment Securities - Unrealized Loss Positions of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	$ 3,146	$ 24,374
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(61)	(281)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	31,676	12,713
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(1,103)	(302)
Securities available-for-sale in a continuous unrealized loss position, total fair value	34,822	37,087
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(1,164)	(583)
US Government Agencies Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	668	6,859
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(3)	(44)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	8,129	2,995
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(186)	(57)
Securities available-for-sale in a continuous unrealized loss position, total fair value	8,797	9,854
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(189)	(101)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	90	15,624
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(1)	(192)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	18,782	7,386
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(595)	(183)
Securities available-for-sale in a continuous unrealized loss position, total fair value	18,872	23,010
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(596)	(375)
Corporate Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	1,953	1,438
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(56)	(42)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	1,299
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(183)
Securities available-for-sale in a continuous unrealized loss position, total fair value	3,252	1,438
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(239)	(42)
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	435	453
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(1)	(3)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	3,466	2,332
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(139)	(62)
Securities available-for-sale in a continuous unrealized loss position, total fair value	3,901	2,785
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	$ (140)	$ (65)