Note 5 - Investment Securities - Gross Unrealized Losses and Fair Value by Investment Category and Continuous Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Securities in continuous unrealized loss position, less than twelve months, number of securities	64	41
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 63,911	$ 51,302
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (1,436)	$ (422)
Securities in continuous unrealized loss position, twelve months or more, number of securities	26	26
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 45,842	$ 46,533
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (2,259)	$ (1,586)
Securities in continuous unrealized loss position, number of securities	90	67
Securities in continuous unrealized loss position, fair value	$ 109,753	$ 97,835
Securities in continuous unrealized loss position, gross unrealized losses	$ (3,695)	$ (2,008)
US Government Agencies Debt Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	7	7
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 23,434	$ 23,805
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (587)	$ (223)
Securities in continuous unrealized loss position, twelve months or more, number of securities	16	16
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 41,494	$ 42,083
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (2,069)	$ (1,492)
Securities in continuous unrealized loss position, number of securities	23	23
Securities in continuous unrealized loss position, fair value	$ 64,928	$ 65,888
Securities in continuous unrealized loss position, gross unrealized losses	$ (2,656)	$ (1,715)
US States and Political Subdivisions Debt Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	42	20
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 23,495	$ 10,061
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (427)	$ (47)
Securities in continuous unrealized loss position, twelve months or more, number of securities	9	9
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 4,295	$ 4,397
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (182)	$ (87)
Securities in continuous unrealized loss position, number of securities	51	29
Securities in continuous unrealized loss position, fair value	$ 27,790	$ 14,458
Securities in continuous unrealized loss position, gross unrealized losses	$ (609)	$ (134)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	9	9
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 16,001	$ 16,978
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (392)	$ (145)
Securities in continuous unrealized loss position, twelve months or more, number of securities
Securities in continuous unrealized loss position, twelve months or more, fair value
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses
Securities in continuous unrealized loss position, number of securities	9	9
Securities in continuous unrealized loss position, fair value	$ 16,001	$ 16,978
Securities in continuous unrealized loss position, gross unrealized losses	$ (392)	$ (145)
Equity Securities - Mutual Funds [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	1
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 495
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (5)
Securities in continuous unrealized loss position, twelve months or more, number of securities
Securities in continuous unrealized loss position, twelve months or more, fair value
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses
Securities in continuous unrealized loss position, number of securities	1
Securities in continuous unrealized loss position, fair value	$ 495
Securities in continuous unrealized loss position, gross unrealized losses	$ (5)
Equity Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	5	5
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 486	$ 458
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (25)	$ (7)
Securities in continuous unrealized loss position, twelve months or more, number of securities	1	1
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 53	$ 53
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (8)	$ (7)
Securities in continuous unrealized loss position, number of securities	6	6
Securities in continuous unrealized loss position, fair value	$ 539	$ 511
Securities in continuous unrealized loss position, gross unrealized losses	$ (33)	$ (14)