Note 8 - Accrued Retirement Benefits - Net Periodic Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest cost	$ 495	$ 560	$ 990	$ 1,120
Expected return on plan assets	(578)	(562)	(1,156)	(1,124)
Amortization of net loss	185	204	370	408
Pension and other postretirement expenses	$ 102	$ 202	$ 204	$ 404