Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Securities in a Continuours Loss Position, Less Than 12 Months, Fair Value	$ 246,525	$ 295,295
Securities in a Continuours Loss Position, Less Than 12 Months, Unrealized Loss	2,832	7,232
Securities in a Continuours Loss Position, 12 Months or More, Fair Value	8,738	2,475
Securities in a Continuours Loss Position, 12 Months or More, Unrealized Loss	83	178
US Government Agencies Debt Securities [Member]
Securities in a Continuours Loss Position, Less Than 12 Months, Fair Value	241,874	260,150
Securities in a Continuours Loss Position, Less Than 12 Months, Unrealized Loss	2,781	6,161
Securities in a Continuours Loss Position, 12 Months or More, Fair Value	7,949	996
Securities in a Continuours Loss Position, 12 Months or More, Unrealized Loss	51	4
US States and Political Subdivisions Debt Securities [Member]
Securities in a Continuours Loss Position, Less Than 12 Months, Fair Value	3,702	31,257
Securities in a Continuours Loss Position, Less Than 12 Months, Unrealized Loss	23	934
Securities in a Continuours Loss Position, 12 Months or More, Fair Value	789	1,316
Securities in a Continuours Loss Position, 12 Months or More, Unrealized Loss	32	148
Corporate Debt Securities [Member]
Securities in a Continuours Loss Position, Less Than 12 Months, Fair Value	949	3,888
Securities in a Continuours Loss Position, Less Than 12 Months, Unrealized Loss	28	137
Securities in a Continuours Loss Position, 12 Months or More, Fair Value	0	0
Securities in a Continuours Loss Position, 12 Months or More, Unrealized Loss	$ 0	0
Other Securities [Member]
Securities in a Continuours Loss Position, Less Than 12 Months, Fair Value		0
Securities in a Continuours Loss Position, Less Than 12 Months, Unrealized Loss		0
Securities in a Continuours Loss Position, 12 Months or More, Fair Value		163
Securities in a Continuours Loss Position, 12 Months or More, Unrealized Loss		$ 26