Note 9 - Defined Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plan [Member]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	6	6	19	18
Expected return on plan assets	(5)	(8)	(15)	(23)
Prior service cost	0	0	0	0
Recognized net actuarial loss	4	2	10	5
Net periodic benefit cost	5	0	14	0
Other Postretirement Benefits Plan [Member]
Service cost	10	9	30	27
Interest cost	12	15	38	43
Expected return on plan assets	0	0	0	0
Prior service cost	(7)	(8)	(23)	(23)
Recognized net actuarial loss	0	0	0	0
Net periodic benefit cost	$ 15	$ 16	$ 45	$ 47