Note 3 - Investment Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities in a continuous loss position, less than 12 months, fair value	$ 69,836	$ 153,888
Securities in a continuous loss position, less than 12 months, unrealized losses	696	4,926
Securities in a continuous loss position, greater than 12 months, fair value	42,675
Securities in a continuous loss position, greater than 12 months, unrealized losses	1,163
Securities in a continuous loss position, fair value	112,511	153,888
Securities in a continuous loss position, unrealized losses	1,859	4,926
US Treasury and Government [Member]
Securities in a continuous loss position, less than 12 months, fair value	2,498	1,969
Securities in a continuous loss position, less than 12 months, unrealized losses	3	31
Securities in a continuous loss position, greater than 12 months, fair value	1,977	0
Securities in a continuous loss position, greater than 12 months, unrealized losses	23	0
Securities in a continuous loss position, fair value	4,475	1,969
Securities in a continuous loss position, unrealized losses	26	31
US States and Political Subdivisions Debt Securities [Member]
Securities in a continuous loss position, less than 12 months, fair value	33,349	73,194
Securities in a continuous loss position, less than 12 months, unrealized losses	491	3,472
Securities in a continuous loss position, greater than 12 months, fair value	14,814
Securities in a continuous loss position, greater than 12 months, unrealized losses	632
Securities in a continuous loss position, fair value	48,163	73,194
Securities in a continuous loss position, unrealized losses	1,123	3,472
Collateralized Mortgage Backed Securities [Member]
Securities in a continuous loss position, less than 12 months, fair value	33,989	78,725
Securities in a continuous loss position, less than 12 months, unrealized losses	202	1,423
Securities in a continuous loss position, greater than 12 months, fair value	25,884	0
Securities in a continuous loss position, greater than 12 months, unrealized losses	508	0
Securities in a continuous loss position, fair value	59,873	78,725
Securities in a continuous loss position, unrealized losses	$ 710	$ 1,423