Note 2 - Investment Securities - Unrealized Loss Positions of Available-for-sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	$ 17,626	$ 25,191
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(139)	(490)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	8,710	5,227
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(198)	(99)
Securities available-for-sale in a continuous unrealized loss position, total fair value	26,336	30,418
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(337)	(589)
US Government Agencies Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	4,513	3,492
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(36)	(32)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	1,984	3,491
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(26)	(64)
Securities available-for-sale in a continuous unrealized loss position, total fair value	6,497	6,983
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(62)	(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	9,394	14,232
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(73)	(235)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	4,404	1,474
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(91)	(30)
Securities available-for-sale in a continuous unrealized loss position, total fair value	13,798	15,706
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(164)	(265)
Corporate Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	2,469	500
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(21)
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	2,469	500
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	(21)
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale in a continuous unrealized loss position, less than 12 months fair value	1,250	6,967
Securities available-for-sale in a continuous unrealized loss position, less than 12 months unrealized loss	(9)	(223)
Securities available-for-sale in a continuous unrealized loss position, 12 months or more fair value	2,322	262
Securities available-for-sale in a continuous unrealized loss position, 12 months or more unrealized loss	(81)	(5)
Securities available-for-sale in a continuous unrealized loss position, total fair value	3,572	7,229
Securities available-for-sale in a continuous unrealized loss position, total unrealized loss	$ (90)	$ (228)