Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Temporarily impaired securities, less than 12 months, fair value	$ 184,244	$ 295,295
Temporarily impaired securities, less than 12 months unrealized loss	1,750	7,232
Temporarily impaired securities, 12 months or more fair value	89,029	2,475
Temporarily impaired securities, 12 months or more unrealized loss	1,553	178
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	176,979	260,150
Temporarily impaired securities, less than 12 months unrealized loss	1,692	6,161
Temporarily impaired securities, 12 months or more fair value	87,469	996
Temporarily impaired securities, 12 months or more unrealized loss	1,513	4
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	6,314	31,257
Temporarily impaired securities, less than 12 months unrealized loss	32	934
Temporarily impaired securities, 12 months or more fair value	1,560	1,316
Temporarily impaired securities, 12 months or more unrealized loss	40	148
Corporate Debt Securities [Member]
Temporarily impaired securities, less than 12 months, fair value	951	3,888
Temporarily impaired securities, less than 12 months unrealized loss	26	137
Temporarily impaired securities, 12 months or more fair value	0	0
Temporarily impaired securities, 12 months or more unrealized loss	$ 0	0
Other Securities [Member]
Temporarily impaired securities, less than 12 months, fair value		0
Temporarily impaired securities, less than 12 months unrealized loss		0
Temporarily impaired securities, 12 months or more fair value		163
Temporarily impaired securities, 12 months or more unrealized loss		$ 26