Note 4 - Investment Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Securities in a continuous loss position, less than 12 months, fair value		$ 153,888
Securities in a continuous loss position, less than 12 months, unrealized losses		4,926
Securities in a continuous loss position, greater than 12 months, fair value
Securities in a continuous loss position, greater than 12 months, unrealized losses
Securities in a continuous loss position, fair value		153,888
Securities in a continuous loss position, unrealized losses		4,926
Securities in a continuous loss position, less than 12 months, fair value	$ 45,944
Securities in a continuous loss position, less than 12 months, unrealized losses	228
Securities in a continuous loss position, greater than 12 months, fair value	63,549
Securities in a continuous loss position, greater than 12 months, unrealized losses	1,361
Securities in a continuous loss position, fair value	109,493
Securities in a continuous loss position, unrealized losses	1,589
US Treasury and Government [Member]
Securities in a continuous loss position, less than 12 months, fair value	494	1,969
Securities in a continuous loss position, less than 12 months, unrealized losses	6	31
Securities in a continuous loss position, greater than 12 months, fair value	1,969
Securities in a continuous loss position, greater than 12 months, unrealized losses	31
Securities in a continuous loss position, fair value	2,463	1,969
Securities in a continuous loss position, unrealized losses	37	31
US States and Political Subdivisions Debt Securities [Member]
Securities in a continuous loss position, less than 12 months, fair value		73,194
Securities in a continuous loss position, less than 12 months, unrealized losses		3,472
Securities in a continuous loss position, greater than 12 months, fair value
Securities in a continuous loss position, greater than 12 months, unrealized losses
Securities in a continuous loss position, fair value		73,194
Securities in a continuous loss position, unrealized losses		3,472
Securities in a continuous loss position, less than 12 months, fair value	14,335
Securities in a continuous loss position, less than 12 months, unrealized losses	55
Securities in a continuous loss position, greater than 12 months, fair value	20,633
Securities in a continuous loss position, greater than 12 months, unrealized losses	384
Securities in a continuous loss position, fair value	34,968
Securities in a continuous loss position, unrealized losses	439
Collateralized Mortgage Backed Securities [Member]
Securities in a continuous loss position, less than 12 months, fair value	31,115	78,725
Securities in a continuous loss position, less than 12 months, unrealized losses	167	1,423
Securities in a continuous loss position, greater than 12 months, fair value	40,947
Securities in a continuous loss position, greater than 12 months, unrealized losses	946
Securities in a continuous loss position, fair value	72,062	78,725
Securities in a continuous loss position, unrealized losses	$ 1,113	$ 1,423