Note 2 - Investment Securities - Unrealized Loss Positions of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Securities available-for-sale in a continuous unrealized loss position, total fair value	$ 21,398	$ 30,418
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(247)	(589)
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	17,265	25,191
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(195)	(490)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	4,133	5,227
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(52)	(99)
US Government Agencies Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, total fair value	3,332	6,983
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(31)	(96)
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	1,466	3,492
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(10)	(32)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	1,866	3,491
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(21)	(64)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale in a continuous unrealized loss position, total fair value	14,297	15,706
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(131)	(265)
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	12,793	14,232
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(112)	(235)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	1,504	1,474
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(19)	(30)
Corporate Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, total fair value	250	500
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	250	500
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, total fair value	3,519	7,229
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(85)	(228)
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	2,756	6,967
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(73)	(223)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	763	262
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	$ (12)	$ (5)