Note 2 - Investment Securities - Unrealized Loss Positions of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	$ 27,478	$ 25,191
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(476)	(490)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	3,522	5,227
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(62)	(99)
Securities available-for-sale in a continuous unrealized loss position, total fair value	31,000	30,418
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(538)	(589)
US Government Agencies Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	3,706	3,492
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(28)	(32)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	2,702	3,491
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(43)	(64)
Securities available-for-sale in a continuous unrealized loss position, total fair value	6,408	6,983
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(71)	(96)
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	18,270	14,232
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(257)	(235)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	161	1,474
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(4)	(30)
Securities available-for-sale in a continuous unrealized loss position, total fair value	18,431	15,706
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(261)	(265)
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	5,502	6,967
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(191)	(223)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	659	262
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(15)	(5)
Securities available-for-sale in a continuous unrealized loss position, total fair value	6,161	7,229
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	$ (206)	(228)
Corporate Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value		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
Securities available-for-sale in a continuous unrealized loss position, total fair value		500
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss