Note 8 - Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Service cost - benefits earned during the period	$ 65	$ 57	$ 48
Interest cost on projected benefit obligation	965	988	951
Expected return on plan assets	(1,218)	(1,188)	(1,343)
Recognized actuarial loss	3,755	1,288
Settlement loss	435	445	460
Net periodic pension cost after settlements	1,289	1,329	888
Recognized Actuarial Loss [Member]
Recognized actuarial loss	$ 1,042	$ 1,027	$ 772