Note 3 - Investment Securities - Gross Unrealized Losses and Fair Value by Investment Category and Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Securities in continuous unrealized loss position, less than twelve months, number of securities	44	64
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 55,195	$ 82,762
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (665)	$ (2,297)
Securities in continuous unrealized loss position, twelve months or more, number of securities	16	1
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 28,135	$ 260
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (759)	$ (2)
Securities in continuous unrealized loss position, number of securities	60	65
Securities in continuous unrealized loss position, fair value	$ 83,330	$ 83,022
Securities in continuous unrealized loss position, gross unrealized losses	$ (1,424)	$ (2,299)
US Government Agencies Debt Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	12	23
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 33,733	$ 62,853
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (525)	$ (1,806)
Securities in continuous unrealized loss position, twelve months or more, number of securities	9
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 24,646
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (717)
Securities in continuous unrealized loss position, number of securities	21	23
Securities in continuous unrealized loss position, fair value	$ 58,379	$ 62,853
Securities in continuous unrealized loss position, gross unrealized losses	$ (1,242)	$ (1,806)
US States and Political Subdivisions Debt Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	22	39
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 11,788	$ 19,749
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (80)	$ (485)
Securities in continuous unrealized loss position, twelve months or more, number of securities	7	1
Securities in continuous unrealized loss position, twelve months or more, fair value	$ 3,489	$ 260
Securities in continuous unrealized loss position, twelve months or more, gross unrealized losses	$ (42)	$ (2)
Securities in continuous unrealized loss position, number of securities	29	40
Securities in continuous unrealized loss position, fair value	$ 15,277	$ 20,009
Securities in continuous unrealized loss position, gross unrealized losses	$ (122)	$ (487)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	4
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 9,191
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (45)
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	4
Securities in continuous unrealized loss position, fair value	$ 9,191
Securities in continuous unrealized loss position, gross unrealized losses	$ (45)
Equity Securities [Member]
Securities in continuous unrealized loss position, less than twelve months, number of securities	6	2
Securities in continuous unrealized loss position, less than twelve months, fair value	$ 483	$ 160
Securities in continuous unrealized loss position, less than twelve months, gross unrealized losses	$ (15)	$ (6)
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	6	2
Securities in continuous unrealized loss position, fair value	$ 483	$ 160
Securities in continuous unrealized loss position, gross unrealized losses	$ (15)	$ (6)